Real image mode finder optical system

ABSTRACT

A real image mode finder optical system is constructed to be independent of a photographing optical system and includes, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the focal length of the objective optical system can be made shorter than that of the eyepiece optical system. In this case, the real image mode finder optical system satisfies the following condition:
 
0.52&lt; mh/fe &lt;1
 
where mh is the maximum width of the field frame and fe is the focal length of the eyepiece optical system.

This application is a divisional of U.S. application Ser. No. 09/836,391filed Apr. 18, 2001, now U.S. Pat. No. 6,671,461 B2.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a real image mode finder optical systemsuitable for use in a lens shutter camera or an electronic still camerawhich is constructed so that a photographing optical system isindependent of a finder optical system, and in particular, to a realimage mode finder optical system which has a large angle of emergenceand is best adapted for mounting to a compact camera.

2. Description of Related Art

In general, finders constructed to be independent of photographingoptical systems, used in lens shutter cameras, are roughly divided intotwo classes: virtual image mode finders and real image mode finders.

The virtual image mode finder has the advantage that an image erectingoptical system is not required, but has the disadvantage that since anentrance pupil is located at the same position as an observer's pupil,the diameter of a front lens must be increased or the area of a visualfield is not defined. An Albada finder of this type allows the area ofthe visual field to be definitely set, but has the problem that a halfmirror coating is applied to the surface of a lens and thus thetransmittance of the lens is reduced or flare is increased.

In contrast to this, the real image mode finder is such that theposition of the entrance pupil can be located on the object side, andhence the diameter of the front lens can be decreased. Moreover, byplacing a field frame in the proximity of the imaging position of anobjective lens, the area of the visual field can be defined withoutreducing the transmittance.

A conventional real image mode finder, however, dose not provide asufficient angle of apparent visual field (hereinafter referred to as anangle of emergence). Specifically, an object to be observed can beviewed only in small size. Thus, when the object is a person, there isthe problem that it is difficult to view the expression of the person. Afinder with a relatively large angle of emergence is disclosed, forexample, in each of Japanese Patent Preliminary Publication Nos. Hei6-51201 and Hei 11-242167. However, even such a finder does not providea sufficiently large angle of emergence.

A so-called telescope has a large angle of emergence. However, thetelescope, which has a high magnification, namely a small angle ofvisual field, cannot be applied to a finder constructed to beindependent of the photographing optical system, used in a common lensshutter camera which has a wide angle of view.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a realimage mode finder optical system in which the angle of emergence can beincreased and compactness can be attained.

In order to achieve this object, the real image mode finder opticalsystem according to the present invention is constructed to beindependent of the photographing optical system and has, in order fromthe object side, an objective optical system with a positive refractingpower, a field frame located in the proximity of the imaging position ofthe objective optical system, and an eyepiece optical system with apositive refracting power. The real image mode finder optical systemincludes an image erecting means, and the focal length of the objectiveoptical system can be made shorter than that of the eyepiece opticalsystem. In this case, the real image mode finder optical systemsatisfies the following condition:0.52<mh/fe<1  (1)where mh is the maximum width of the field frame and fe is the focallength of the eyepiece optical system.

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system includes three of reflecting surfaces of theimage erecting means, and the eyepiece optical system includes one ofreflecting surfaces of the image erecting means so that an image iserected through four reflecting surfaces comprised of three reflectingsurfaces of the objective optical system and one reflecting surface ofthe eyepiece optical system. The focal length of the objective opticalsystem is variable, and when the magnification of the finder opticalsystem is changed, at least two lens units are moved along differentpaths. The focal length of the objective optical system at thewide-angle position thereof is shorter than that of the eyepiece opticalsystem. In this case, the real image mode finder optical systemsatisfies Condition (1).

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system includes three of reflecting surfaces of theimage erecting means, and the eyepiece optical system includes one ofreflecting surfaces of the image erecting means so that an image iserected through four reflecting surfaces comprised of three reflectingsurfaces of the objective optical system and one reflecting surface ofthe eyepiece optical system. The focal length of the objective opticalsystem is variable, and when the magnification of the finder opticalsystem is changed, at least two lens units are moved along differentpaths. The focal length of the objective optical system at thewide-angle position thereof is shorter than that of the eyepiece opticalsystem. The image erecting means including the three reflecting surfacesis constructed with two prisms so that each of the prisms has at leastone reflecting surface and one of the entrance surface and the exitsurface of each prism is configured as a curved surface with finitecurvature.

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. Theobjective optical system has an image erecting means including fourreflecting surfaces. The focal length of the objective optical system isvariable, and when the magnification of the finder optical system ischanged, at least two lens units are moved along different paths. Thefocal length of the objective optical system at the wide-angle positionthereof is shorter than that of the eyepiece optical system. In thiscase, the real image mode finder optical system satisfies Condition (1).

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. Theobjective optical system has an image erecting means including fourreflecting surfaces. The focal length of the objective optical system isvariable, and when the magnification of the finder optical system ischanged, at least two lens units are moved along different paths. Thefocal length of the objective optical system at the wide-angle positionthereof is shorter than that of the eyepiece optical system.

This and other objects as well as the features and advantages of thepresent invention will become apparent from the following detaileddescription of the preferred embodiments when taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing of a first embodiment of the realimage mode finder optical system according to the present invention;

FIG. 2 is a plan view of the real image mode finder optical system ofFIG. 1;

FIG. 3 is a side view of the real image mode finder optical system ofFIG. 1;

FIG. 4 is an explanatory view of a field frame used in the real imagemode finder optical system of the first embodiment;

FIGS. 5A, 5B, and 5C are sectional views showing arrangements, developedalong the optical axis, at wide-angle, middle, and telephoto positions,respectively, of the real image mode finder optical system in the firstembodiment;

FIGS. 6A, 6B, 6C, and 6D are diagrams showing aberration characteristicsat the wide-angle position of the real image mode finder optical systemin the first embodiment;

FIGS. 7A, 7B, 7C, and 7D are diagrams showing aberration characteristicsat the middle position of the real image mode finder optical system inthe first embodiment;

FIGS. 8A, 8B, 8C, and 8D are diagrams showing aberration characteristicsat the telephoto position of the real image mode finder optical systemin the first embodiment;

FIGS. 9A, 9B, and 9C are sectional views showing arrangements, developedalong the optical axis, at wide-angle, middle, and telephoto positions,respectively, of the real image mode finder optical system in a secondembodiment;

FIGS. 10A, 10B, 10C, and 10D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the second embodiment;

FIGS. 11A, 11B, 11C, and 11D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the second embodiment;

FIGS. 12A, 12B, 12C, and 12D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the second embodiment;

FIGS. 13A, 13B, and 13C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina third embodiment;

FIGS. 14A, 14B, 14C, and 14D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the third embodiment;

FIGS. 15A, 15B, 15C, and 15D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the third embodiment;

FIGS. 16A, 16B, 16C, and 16D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the third embodiment;

FIGS. 17A, 17B, and 17C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fourth embodiment;

FIGS. 18A, 18B, 18C, and 18D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the fourth embodiment;

FIGS. 19A, 19B, 19C, and 19D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the fourth embodiment;

FIGS. 20A, 20B, 20C, and 20D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the fourth embodiment;

FIGS. 21A, 21B, and 21C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fifth embodiment;

FIGS. 22A, 22B, 22C, and 22D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the fifth embodiment;

FIGS. 23A, 23B, 23C, and 23D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the fifth embodiment;

FIGS. 24A, 24B, 24C, and 24D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the fifth embodiment;

FIGS. 25A, 25B, 25C, and 25D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in a sixth embodiment;

FIGS. 26A, 26B, 26C, and 26D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the sixth embodiment;

FIGS. 27A, 27B, 27C, and 27D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the sixth embodiment;

FIGS. 28A, 28B, 28C, and 28D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the sixth embodiment;

FIGS. 29A, 29B, 29C, and 29D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the sixth embodiment;

FIGS. 30A, 30B, 30C, and 30D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in a seventh embodiment;

FIGS. 31A, 31B, 31C, and 31D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the seventh embodiment;

FIGS. 32A, 32B, 32C, and 32D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the seventh embodiment;

FIGS. 33A, 33B, 33C, and 33D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the seventh embodiment;

FIGS. 34A, 34B, 34C, and 34D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the seventh embodiment;

FIGS. 35A, 35B, 35C, and 35D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in an eighth embodiment;

FIGS. 36A, 36B, 36C, and 36D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the eighth embodiment;

FIGS. 37A, 37B, 37C, and 37D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the eighth embodiment;

FIGS. 38A, 38B, 38C, and 38D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the eighth embodiment;

FIGS. 39A, 39B, 39C, and 39D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the eighth embodiment;

FIGS. 40A, 40B, 40C, and 40D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in a ninth embodiment;

FIGS. 41A, 41B, 41C, and 41D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the ninth embodiment;

FIGS. 42A, 42B, 42C, and 42D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the ninth embodiment;

FIGS. 43A, 43B, 43C, and 43D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the sixth embodiment;

FIGS. 44A, 44B, 44C, and 44D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the ninth embodiment;

FIGS. 45A, 45B, 45C, and 45D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in a tenth embodiment;

FIGS. 46A, 46B, 46C, and 46D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the tenth embodiment;

FIGS. 47A, 47B, 47C, and 47D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the tenth embodiment;

FIGS. 48A, 48B, 48C, and 48D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the tenth embodiment;

FIGS. 49A, 49B, 49C, and 49D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the tenth embodiment;

FIGS. 50A, 50B, 50C, and 50D are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions and with respect to an eyepiece optical system, respectively,of the real image mode finder optical system in an eleventh embodiment;

FIGS. 51A, 51B, 51C, and 51D are diagrams showing aberrationcharacteristics at the wide-angle position of the real image mode finderoptical system in the eleventh embodiment;

FIGS. 52A, 52B, 52C, and 52D are diagrams showing aberrationcharacteristics at the middle position of the real image mode finderoptical system in the eleventh embodiment;

FIGS. 53A, 53B, 53C, and 53D are diagrams showing aberrationcharacteristics at the telephoto position of the real image mode finderoptical system in the eleventh embodiment;

FIGS. 54A, 54B, 54C, and 54D are diagrams showing aberrationcharacteristics of the eyepiece optical system of the real image modefinder optical system in the eleventh embodiment;

FIGS. 55A, 55B, and 55C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twelfth embodiment;

FIGS. 56A, 56B, and 56C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina thirteenth embodiment;

FIGS. 57A, 57B, and 57C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fourteenth embodiment;

FIGS. 58A, 58B, and 58C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina fifteenth embodiment;

FIGS. 59A, 59B, and 59C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina sixteenth embodiment;

FIGS. 60A, 60B, and 60C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina seventeenth embodiment;

FIGS. 61A, 61B, and 61C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system inan eighteenth embodiment;

FIGS. 62A, 62B, and 62C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina nineteenth embodiment;

FIGS. 63A, 63B, and 63C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twentieth embodiment;

FIGS. 64A, 64B, and 64C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-first embodiment;

FIG. 65 is a plan view of the real image mode finder optical system inthe twenty-first embodiment;

FIG. 66 is a side view of the real image mode finder optical system ofFIG. 65;

FIG. 67 is a rear view of the real image mode finder optical system ofFIG. 65;

FIGS. 68A, 68B, and 68C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-second embodiment;

FIGS. 69A, 69B, and 69C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-third embodiment;

FIGS. 70A, 70B, and 70C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of the real image mode finder optical system ina twenty-fourth embodiment;

FIG. 71 is a front perspective view showing the appearance of anelectronic camera in an embodiment of a photographing apparatus usingthe real image mode finder optical system of the present invention:

FIG. 72 is a rear perspective view of the electronic camera of FIG. 71;

FIG. 73 is a sectional view showing the structure of the electroniccamera of FIG. 71; and

FIGS. 74A, 74B, and 74C are sectional views showing arrangements,developed along the optical axis, at wide-angle, middle, and telephotopositions, respectively, of a photographing zoom lens used in a compactcamera for a 35 mm film (the maximum image height of 21.6 mm).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, when the objective optical system isdesigned to have the focal length shorter than that of the eyepieceoptical system, the magnification of the real image mode finer opticalsystem can be reduced to 1× or less, and as a result, the angle ofvisual field can be increased.

Condition (1) in the present invention is related to the angle ofemergence. In order to increase the angle of emergence, it is onlynecessary to increase the size of an image obtained by the objectiveoptical system, that is, the size of the field frame, or to reduce thefocal length of the eyepiece optical system.

Below the lower limit of Condition (1), the image can be seen only insmall size. On the other hand, beyond the upper limit of Condition (1),it becomes difficult to grasp the entire area of the visual field, forexample, to quickly determine a picture composition.

By constructing the finder optical system to be independent of thephotographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

It is desirable that the real image mode finder optical system of thepresent invention satisfies the following condition:12.0 mm<fe<18.0 mm  (2)

Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

If the lower limit of Condition (2) is passed, a distance on the opticalaxis between the front principal point of the eyepiece optical systemand the field frame will be reduced and at the same time, the findermagnification will be as low as 1× or less. Therefore, a distance on theoptical axis between the rear principal point of the objective opticalsystem and the field frame is also reduced, and it becomes difficult toplace the image erecting means, which is not favorable.

On the other hand, beyond the upper limit of Condition (2), the maximumwidth mh of the field frame must be enlarged to increase the angle ofemergence. In this case, the objective optical system becomes bulky andthe balance between the angle of emergence and the size of the realimage mode finder ceases to be kept, which is unfavorable.

It is more desirable that the real image mode finder optical systemsatisfies the following condition:13.5 mm<fe<16.5 mm  (3)

It is favorable that the real image mode finder optical system isconstructed so that the objective optical system includes threereflecting surfaces of the image erecting means and the eyepiece opticalsystem includes one reflecting surface of the image erecting means toerect an image with four reflecting surfaces comprised of the threereflecting surfaces of the objective optical system and the onereflecting surface of the eyepiece optical system.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When three offour reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,a real image mode finder optical system with a large angle of emergencecan be constructed in a state where the arrangement of the eyepieceoptical system is simplified.

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the objective optical systemhas the image erecting means including four reflecting surfaces to erectthe image with the four reflecting surfaces of the objective opticalsystem.

In this case, at least four reflecting surfaces are required for theimage erecting means, and thus if the image erecting means isconstructed with four reflecting surfaces, space efficiency can beimproved. When the image erecting means is placed in the objectiveoptical system, the burden of a space for placing the image erectingmeans to the eyepiece optical system is eliminated, and the eyepieceoptical system can be constructed with a small number of lenses.Consequently, the focal length of the eyepiece optical system can becompletely reduced, and aberration characteristics are easily improved.Thus, according to the present invention, a real image mode finderoptical system with a large angle of emergence can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

As mentioned above, when the objective optical system is designed tohave the focal length shorter than that of the eyepiece optical system,the magnification of the real image mode finer optical system can bereduced to 1× or less, and as a result, the angle of visual field can beincreased. Condition (1) in the present invention is related to theangle of emergence.

Below the lower limit of Condition (1), the image can be seen only insmall size. On the other hand, beyond the upper limit of Condition (1),it becomes difficult to grasp the entire area of the visual field, forexample, to quickly determine a picture composition.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When three offour reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Also, theobjective optical system has a large number of lenses because of themagnification change, and hence can be designed to ensure a space forincorporating three reflecting surfaces in the objective optical system.Consequently, a real image mode finder optical system which has a largeangle of emergence and is compact in design can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

It is desirable that the real image mode finder optical system of thepresent invention is constructed so that the objective optical systemcomprises, in order from the object side, a first unit with a negativepower, fixed or moved when the magnification is changed; a second unitwith a positive power, moved when the magnification is changed; a thirdunit with a negative power, moved when the magnification is changed; anda fourth unit with a positive power, fixed when the magnification ischange and including three reflecting surfaces.

According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical systemand to obtain favorable aberration and a large angle of emergence.

It is desirable that the real image mode finder optical system of thepresent invention is constructed so that the fourth unit includes atleast one prism having at least one reflecting surface, and one of theentrance surface and the exit surface of the prism is configured as acurved surface with finite curvature.

According to the present invention, a lens function, such as acontribution to the focal length or correction for aberration, as thefourth unit of the objective optical system and an image erectingfunction can be exerted in the same space.

Furthermore, it is desirable that the real image mode finder opticalsystem of the present invention is constructed so that one of thereflecting surfaces of the prism is configured as a totally reflectingsurface.

If total reflection is utilized as far as possible with respect to thereflecting surfaces of the prism, the transmittance of the entire findercan be improved accordingly.

In the real image mode finder optical system, it is desirable that eachof the first unit, the second unit, and the third unit is constructedwith a single lens.

According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical system.

Moreover, it is desirable that the real image mode finder optical systemof the present invention is constructed so that the eyepiece opticalsystem includes optical elements having two lens functions, providingair spacing between them and has a positive refracting power as a whole.

In order to increase the angle of emergence, it is only necessary toincrease the size of an image obtained by the objective optical system,that is, the size of the field frame, or to reduce the focal length ofthe eyepiece optical system. However, if the field frame is enlargedwith respect to the focal length of the eyepiece optical system, theburden of correction for aberration to the eyepiece optical system willbe increased, and it becomes difficult to hold good performance with asingle lens. If three or more optical elements are used, it becomesdifficult to obtain compactness of the whole of the real image modefinder optical system. Hence, in order to diminish the size of theentire system including the objective optical system, it is desirable toreduce the focal length of the eyepiece optical system. However, whenthe focal length of the eyepiece optical system is reduced, the distanceon the optical axis between the front principal point of the eyepieceoptical system and the field frame is diminished, and, for example,space for arranging the optical elements of the image erecting means isnarrowed.

Thus, in view of good performance, space for placing the image erectingmeans, and compactness of the whole of the real image mode finderoptical system, it is desirable that the eyepiece optical system, asmentioned above, is constructed with the optical elements having twolens functions, providing air spacing between them.

Furthermore, it is desirable that the real image mode finder opticalsystem of the present invention is designed so that the eyepiece opticalsystem includes, in order from the object side, a prism which has thelens function, at least, with respect to the exit surface and bears apart of an image erecting function and a single positive lens component.

As mentioned above, when an optical element on the field frame side ofthe eyepiece optical system is constructed with the prism which bears apart of the image erecting function, space can be effectively utilized.Moreover, when the lens function is imparted to the prism separated fromthe field frame, the degree of a contribution to the focal length of theeyepiece optical system is increased, and it becomes easy to reduce thefocal length of the eyepiece optical system.

It is desirable that the real image mode finder optical system of thepresent invention is designed to impart the lens function to theentrance surface of the prism of the eyepiece optical system.

Since the entrance surface of the prism of the eyepiece optical systemis located close to the field frame, the degree of a contribution to thefocal length of the eyepiece optical system is low. However, correctionfor aberration, notably for distortion, and a pupil combination of theobjective optical system and the eyepiece optical system are favorablycompatible.

It is desirable that the real image mode finder optical system isdesigned so that the reflecting surface of the prism of the eyepieceoptical system is configured as a totally reflecting surface.

As described above, when total reflection is utilized for the reflectingsurface of the prism, the transmittance of the entire system of thefinder can be improved accordingly.

It is desirable that the real image mode finder optical system of thepresent invention is constructed so that the positive lens of theeyepiece optical system is capable of making diopter adjustment inaccordance with an observer's diopter.

According to the present invention, a change of the diopter required isobtained with a small amount of adjustment. Since the diopter can beadjusted by the positive lens, unlike an element in which the opticalaxis is bent as in the prism, the adjustment can be easily made.

In this case, it is favorable that the real image mode finder opticalsystem of the present invention satisfies Condition (2).

Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

If the lower limit of Condition (2) is passed, a distance on the opticalaxis between the front principal point of the eyepiece optical systemand the field frame will be reduced and at the same time, the findermagnification will be as low as 1× or less. Therefore, a distance on theoptical axis between the rear principal point of the objective opticalsystem and the field frame is also reduced, and it becomes difficult toplace the image erecting means, which is not favorable.

On the other hand, beyond the upper limit of Condition (2), the maximumwidth mh of the field frame must be enlarged to increase the angle ofemergence. In this case, the objective optical system becomes bulky andthe balance between the angle of emergence and the size of the realimage mode finder ceases to be kept, which is unfavorable.

It is more desirable that the real image mode finder optical systemsatisfies Condition (3).

According to the present invention, when the objective optical system isdesigned to have the focal length shorter than that of the eyepieceoptical system, the magnification of the real image mode finer opticalsystem can be reduced to 1× or less, and as a result, the angle ofvisual field can be increased.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When three offour reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Also, theobjective optical system has a large number of lenses because of themagnification change, and hence can be designed to ensure a space forincorporating three reflecting surfaces in the objective optical system.Consequently, a real image mode finder optical system which has a largeangle of emergence and is compact in design can be constructed in astate where the arrangement of the eyepiece optical system issimplified.

The image erecting means including the three reflecting surfaces isconstructed with two prisms so that each of the prisms has at least onereflecting surface and one of the entrance surface and the exit surfaceof each prism is configured as a curved surface with finite curvature.

When the image erecting means including the three reflecting surfaces ofthe objective optical system is constructed with two prisms so that oneof the entrance surface and the exit surface of each prism has acurvature, a lens function, such as a contribution to the focal lengthor correction for aberration, and an image erecting function can beexerted in the same space.

As mentioned above, when the objective optical system is designed tohave the focal length shorter than that of the eyepiece optical system,the magnification of the real image mode finer optical system can bereduced to 1× or less, and as a result, the angle of visual field can beincreased. Condition (1) in the present invention is related to theangle of emergence.

Below the lower limit of Condition (1), the image can be seen only insmall size. On the other hand, beyond the upper limit of Condition (1),it becomes difficult to grasp the entire area of the visual field, forexample, to quickly determine a picture composition.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When the imageerecting means is placed in the objective optical system, the burden ofa space for placing the image erecting means to the eyepiece opticalsystem is eliminated, and the eyepiece optical system can be constructedwith a small number of lenses. Consequently, the focal length of theeyepiece optical system can be completely reduced, and aberrationcharacteristics are easily improved.

Also, the objective optical system has a large number of lenses becauseof the magnification change, and hence the image erecting means can beconstructed with comparative ease.

It is desirable that the real image mode finder optical system of thepresent invention is constructed so that the objective optical systemcomprises, in order from the object side, s first unit with a negativerefracting power, moved when the magnification is changed; a second unitwith a positive refracting power, moved when the magnification ischanged; a third unit with a negative refracting power, moved when themagnification is changed; and a fourth unit with a positive refractingpower, fixed when the magnification is change and including fourreflecting surfaces.

According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical systemand to obtain favorable aberration and a large angle of emergence. Also,the four reflecting surfaces of the fourth unit constitute the imageerecting means.

In the real image mode finder optical system, it is desirable that thefourth unit includes two prisms so that each of the prisms has at leastone reflecting surface and one of the entrance surface and the exitsurface of each prism is configured as a curved surface with finitecurvature.

According to the present invention, a lens function, such as acontribution to the focal length or correction for aberration, as thefourth unit of the objective optical system and an image erectingfunction can be exerted in the same space.

Furthermore, it is desirable that the real image mode finder opticalsystem of the present invention is constructed so that one of the twoprisms has totally reflecting surfaces.

As mentioned above, when total reflection is utilized as far as possiblewith respect to the reflecting surfaces of the prism, the transmittanceof the entire finder can be improved accordingly.

In the real image mode finder optical system, it is desirable that eachof the first unit, the second unit, and the third unit is constructedwith a single lens.

According to the present invention, it becomes easy to achievecompactness of the whole of the real image mode finder optical system.

It is desirable that the real image mode finder optical system of thepresent invention is constructed so that the eyepiece optical system hasa lens which is capable of making diopter adjustment to an observer'sdiopter.

According to the present invention, a change of the diopter required isobtained with a small amount of adjustment, with little deterioration ofperformance. Since the diopter can be adjusted by the lens, unlike anelement in which the optical axis is bent as in the prism, theadjustment can be easily made.

In this case, it is favorable that the real image mode finder opticalsystem of the present invention satisfies Condition (2).

Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

If the lower limit of Condition (2) is passed, a distance on the opticalaxis between the front principal point of the eyepiece optical systemand the field frame will be reduced and at the same time, the findermagnification will be as low as 1× or less. Therefore, a distance on theoptical axis between the rear principal point of the objective opticalsystem and the field frame is also reduced, and it becomes difficult toplace the image erecting means, which is not favorable.

On the other hand, beyond the upper limit of Condition (2), the maximumwidth mh of the field frame must be enlarged to increase the angle ofemergence. In this case, the objective optical system becomes bulky andthe balance between the angle of emergence and the size of the realimage mode finder ceases to be kept, which is unfavorable.

In this case, it is more desirable that the real image mode finderoptical system satisfies Condition (3).

According to the present invention, when the objective optical system isdesigned to have the focal length shorter than that of the eyepieceoptical system, the magnification of the real image mode finer opticalsystem can be reduced to 1× or less, and as a result, the angle ofvisual field can be increased.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When the imageerecting means is placed in the objective optical system, the burden ofa space for placing the image erecting means to the eyepiece opticalsystem is eliminated, and the eyepiece optical system can be constructedwith a small number of lenses. According to the present invention, thefocal length of the eyepiece optical system can be completely reduced,and aberration characteristics are easily improved. Also, the objectiveoptical system has a large number of lenses because of the magnificationchange, and hence the image erecting means can be constructed withcomparative ease.

It is favorable that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system is capable of having the focal length shorterthan that of the eyepiece optical system, and the eyepiece opticalsystem has at least one lens. In this case, a most observer's pupil-sidelens satisfies the following condition:ν>70  (4)where ν is the Abbe's number of the most observer's pupil-side lens.

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system is capable of having the focal length shorterthan that of the eyepiece optical system, and the eyepiece opticalsystem has at least one lens. In this case, the real image mode finderoptical system satisfies Conditions (1) and (4).

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system is capable of having the focal length shorterthan that of the eyepiece optical system, and the eyepiece opticalsystem has a cemented lens component including a positive lens elementand a negative lens element at the most observer's pupil-side position.

When the objective optical system is designed to have the focal lengthshorter than that of the eyepiece optical system, the magnification ofthe real image mode finer optical system can be reduced to 1× or less,and as a result, the angle of visual field can be increased.

When Condition (4) is satisfied, chromatic aberration of magnificationproduced in the eyepiece optical system can be suppressed.

By constructing the finder optical system to be independent of thephotographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

When the objective optical system is designed to have the focal lengthshorter than that of the eyepiece optical system, the magnification ofthe real image mode finer optical system can be reduced to 1× or less,and as a result, the angle of visual field can be increased. Condition(1) in the present invention is related to the angle of emergence. Inorder to increase the angle of emergence, it is only necessary toincrease the size of an image obtained by the objective optical system,that is, the size of the field frame, or to reduce the focal length ofthe eyepiece optical system.

Below the lower limit of Condition (1), the image can be seen only insmall size. On the other hand, beyond the upper limit of Condition (1),it becomes difficult to grasp the entire area of the visual field, forexample, to quickly determine a picture composition.

When Condition (4) is satisfied, chromatic aberration of magnificationproduced in the eyepiece optical system can be suppressed.

By constructing the finder optical system to be independent of thephotographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

It is desirable that the real image mode finder optical system of thepresent invention satisfies Condition (2).

Condition (2) is provided for the purpose of ensuring a space forplacing the image erecting means and compactness of the whole of thereal image mode finder optical system in a state where Condition (1) issatisfied.

If the lower limit of Condition (2) is passed, a distance on the opticalaxis between the front principal point of the eyepiece optical systemand the field frame will be reduced and at the same time, the findermagnification will be as low as 1× or less. Therefore, a distance on theoptical axis between the rear principal point of the objective opticalsystem and the field frame is also reduced, and it becomes difficult toplace the image erecting means, which is not favorable.

On the other hand, beyond the upper limit of Condition (2), the maximumwidth mh of the field frame must be enlarged to increase the angle ofemergence. In this case, the objective optical system becomes bulky andthe balance between the angle of emergence and the size of the realimage mode finder ceases to be kept, which is unfavorable.

It is more desirable that the real image mode finder optical systemsatisfies Condition (3).

It is favorable that the real image mode finder optical system isconstructed so that the objective optical system includes threereflecting surfaces of the image erecting means and the eyepiece opticalsystem includes one reflecting surface of the image erecting means toerect an image with four reflecting surfaces comprised of the threereflecting surfaces of the objective optical system and the onereflecting surface of the eyepiece optical system.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When three offour reflecting surfaces constituting the image erecting means areplaced in the objective optical system, the burden of a space forplacing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced. Thus, according to the present invention,the focal length of the eyepiece optical system can be completelyreduced, and aberration characteristics are easily improved. Inparticular, where the focal length of the objective optical system isvariable, the objective optical system, which has a large number oflenses, can be designed to ensure a space for incorporating threereflecting surfaces in the objective optical system. Consequently, areal image mode finder optical system which has a large angle ofemergence and is compact in design can be constructed in a state wherethe arrangement of the eyepiece optical system is simplified.

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the objective optical systemhas the image erecting means including four reflecting surfaces to erectthe image with the four reflecting surfaces of the objective opticalsystem.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. When the imageerecting means is placed in the objective optical system, the burden ofa space for placing the image erecting means to the eyepiece opticalsystem is eliminated, and the eyepiece optical system can be constructedwith a small number of lenses. According to the present invention, thefocal length of the eyepiece optical system can be completely reduced,and aberration characteristics are easily improved. In particular, wherethe focal length of the objective optical system is variable, the numberof lenses constituting the objective optical system is large, and hencethe image erecting means can be constructed with comparative ease.

According to the present invention, when the objective optical system isdesigned to have the focal length shorter than that of the eyepieceoptical system, the magnification of the real image mode finer opticalsystem can be reduced to 1× or less, and as a result, the angle ofvisual field can be increased.

When the cemented lens component including the positive lens element andthe negative lens element is placed on the observer's pupil side of theeyepiece optical system, chromatic aberration of magnification producedin the eyepiece optical system can be suppressed.

Also, by constructing the finder optical system to be independent of thephotographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

The real image mode finder optical system according to the presentinvention is constructed to be independent of the photographing opticalsystem and has, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system includes an image erecting means, theobjective optical system is capable of having the focal length shorterthan that of the eyepiece optical system, and the eyepiece opticalsystem has a cemented lens component including a positive lens elementand a negative lens element on the observer's pupil side. In this case,it is favorable to satisfy Condition (1).

When the objective optical system is designed to have the focal lengthshorter than that of the eyepiece optical system, the magnification ofthe real image mode finer optical system can be reduced to 1× or less,and as a result, the angle of visual field can be increased. Condition(1) in the present invention is related to the angle of emergence. Inorder to increase the angle of emergence, it is only necessary toincrease the size of an image obtained by the objective optical system,that is, the size of the field frame, or to reduce the focal length ofthe eyepiece optical system.

Below the lower limit of Condition (1), the image can be seen only insmall size. On the other hand, beyond the upper limit of Condition (1),it becomes difficult to grasp the entire area of the visual field, forexample, to quickly determine a picture composition.

When the cemented lens component including the positive lens element andthe negative lens element is placed on the observer's pupil side of theeyepiece optical system, chromatic aberration of magnification producedin the eyepiece optical system can be suppressed.

Also, by constructing the finder optical system to be independent of thephotographing optical system, the value of a maximum width mh of thefield frame can be set, irrespective of the size of an imaging plane.This is particularly advantageous for compact design of the eyepieceoptical system and for the placement of an image erecting means.

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the focal length of theobjective optical system is variable, and when the magnification of thefinder is changed, at least two lens units are moved along differentpaths.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

It is also favorable that the real image mode finder optical system ofthe present invention satisfies the following condition:νp−νn>10  (5)where νp is the Abbe's number of the positive lens element constitutingthe cemented lens component on the observer's pupil side of the eyepieceoptical system and νn is the Abbe's number of the negative lens elementconstituting the cemented lens component.

As mentioned above, when the finder optical system is designed tosatisfy Condition (5), chromatic aberration of magnification produced inthe eyepiece optical system can be suppressed.

It is more desirable that the real image mode finder optical system ofthe present invention satisfies the following condition:νp−νn>20  (6)

It is favorable that that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system has an image erecting means, and theobjective optical system includes, in order from the object side, afirst unit with a negative refracting power, a second unit with apositive refracting power, a third unit with a negative refractingpower, and a fourth unit with a positive refracting power so that themagnification of the finder is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece opticalsystem. In this case, the finder optical system satisfies Condition (2).

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system has an image erecting means, and theobjective optical system includes, in order from the object side, afirst unit with a negative refracting power, a second unit with apositive refracting power, a third unit with a negative refractingpower, and a fourth unit with a positive refracting power so that themagnification of the finder is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece opticalsystem. In this case, the finder optical system satisfies Condition (1).

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem with a positive refracting power, a field frame located in theproximity of the imaging position of the objective optical system, andan eyepiece optical system with a positive refracting power. The realimage mode finder optical system has an image erecting means, and theobjective optical system is capable of having the focal length shorterthan that of the eyepiece optical system. The eyepiece optical systemincludes, in order from the object side, a prism unit with a positiverefracting power and a lens unit with a positive refracting power sothat a most field-frame-side surface of the prism unit with a positiverefracting power has a positive refracting power and is configured as anaspherical surface with a negative refracting power on the peripherythereof.

In order to increase the angle of emergence, it is only necessary toincrease the size of an image obtained by the objective optical system,that is, the size of the field frame, or to reduce the focal length ofthe eyepiece optical system. However, if the field frame is enlargedwith respect to the focal length of the eyepiece optical system, theobjective optical system must be also enlarged. Moreover, since theburden of correction for aberration to the eyepiece optical system willbe increased, it becomes difficult that good performance of the eyepieceoptical system and compactness due to a simple arrangement arecompatible with each other. Thus, in order to keep the size of thefinder compact and increase the angle of emergence, it is desirable toreduce the focal length of the eyepiece optical system.

However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

Thus, in the present invention, the objective optical system is designedto have, in order to the object side, the first unit with a negativerefracting power, the second unit with a positive refracting power, thethird unit with a negative refracting power, and the fourth unit with apositive refracting power. In this way, the back focal distance of theobjective optical system is increased.

When the objective optical system is constructed as mentioned above, thefocal length of the eyepiece optical system can be reduced, and a realimage mode finder optical system which has a large angle of emergenceand is compact in design can be obtained.

Condition (2) defines a condition for maintaining the balance of sizebetween the angle of emergence and the finder. Below the lower limit ofCondition (2), the distance on the optical axis between the frontprincipal point of the eyepiece optical system and the field frame isreduced, and it becomes difficult to ensure the space for placing theimage erecting means. In addition, a diopter shift due to the positionshift of the field frame in the direction of the optical axis isincreased.

On the other hand, beyond the upper limit of Condition (2), theobjective optical system becomes bulky because the image formed byobjective optical system must be enlarged to increase the angle ofemergence. Consequently, the balance between the angle of emergence andthe size of the finder ceases to be kept, which is unfavorable.

When the magnification of the finder is changed, it is necessary that avariable magnification function is chiefly imparted to one of at leasttwo moving lens units and a diopter correcting function involved in themagnification change is chiefly imparted to the other. In this case, theamount of movement of the lens unit having the variable magnificationfunction becomes larger than that of the lens unit having the dioptercorrecting function, and a mechanism for movement is liable to becomplicated and oversized.

Thus, in the present invention, the finder optical system is constructedso that the magnification is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece side.

By doing so, both the variable magnification function and the dioptercorrecting function can be shared between the second unit and the thirdunit. Hence, the amount of movement of each of the second and thirdunits where the magnification is change can be kept to a minimum, andcompactness of the mechanism for movement is obtained.

In this case, it is more desirable that the real image mode finderoptical system satisfies Condition (3).

As mentioned above, in order to increase the angle of emergence, it isonly necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

Thus, in the present invention, the objective optical system is designedto have, in order to the object side, the first unit with a negativerefracting power, the second unit with a positive refracting power, thethird unit with a negative refracting power, and the fourth unit with apositive refracting power. In this way, the back focal distance of theobjective optical system is increased.

When the objective optical system is constructed as mentioned above, thefocal length of the eyepiece optical system can be reduced, and a realimage mode finder optical system which has a large angle of emergenceand is compact in design can be obtained.

Condition (1) is related to the angle of emergence. Below the lowerlimit of Condition (1), the image can be seen only in small size. On theother hand, beyond the upper limit of Condition (1), it becomesdifficult to grasp the entire area of the visual field, for example, toquickly determine a picture composition.

When the magnification of the finder is changed, it is necessary thatthe variable magnification function is chiefly imparted to one of atleast two moving lens units and the diopter correcting function involvedin the magnification change is chiefly imparted to the other. In thiscase, the amount of movement of the lens unit having the variablemagnification function becomes larger than that of the lens unit havingthe diopter correcting function, and a mechanism for movement is liableto be complicated and oversized.

Thus, in the present invention, the finder optical system is constructedso that the magnification is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece opticalsystem.

By doing so, both the variable magnification function and the dioptercorrecting function can be shared between the second unit and the thirdunit. Hence, the amount of movement of each of the second and thirdunits where the magnification is change can be kept to a minimum, andcompactness of the mechanism for movement is obtained.

In this case, it is more desirable that the present invention satisfiesthe following condition:0.57<mh/fe<1  (7)

As described above, when the objective optical system is designed tohave the focal length shorter than that of the eyepiece optical system,the magnification of the real image mode finer optical system can bereduced to 1× or less, and as a result, the angle of visual field can beincreased.

When the eyepiece optical system is designed to have the prism unit, apart of the image erecting means can be shared to the eyepiece opticalsystem, and space can be effectively utilized. When the eyepiece opticalsystem is constructed with the unit having a positive refracting power,the diopter can be adjusted in accordance with the observer's diopter.

In order to keep the size of the finder compact and increase the angleof emergence, it is desirable to reduce the focal length of the eyepieceoptical system. Further, in order to reduce the focal length of theeyepiece optical system, it is desirable to increase the positiverefracting power of the optical element constituting the eyepieceoptical system.

However, if the most field-frame-side surface of the eyepiece opticalsystem is configured so that the positive refracting power is increased,and a marginal beam in the proximity of the field frame is renderednearly parallel to the optical axis, the size of the eyepiece opticalsystem in its radial direction will be increased. On the other hand, ifthe most field-frame-side surface of the eyepiece optical system isconfigured so that the positive refracting power is increased, and atthe same time, the size of the eyepiece optical system in its radialdirection is diminished, the angle of inclination will be increased.Consequently, the marginal beam of the first unit at the wide-angleposition is separated from the optical axis, and hence the diameter ofthe first unit must be enlarged.

Thus, when the most field-frame-side surface of the eyepiece opticalsystem has a positive refracting power and is configured as anaspherical surface with a negative refracting power on its periphery,the diameter of the first unit can be diminished. Moreover, correctionfor aberration, notably for distortion, is favorably compatible with apupil combination of the objective optical system and the eyepieceoptical system, notably in an off-axis.

In the real image mode finder optical system of the present invention,it is desirable that the eyepiece optical system includes, in order fromthe object side, a prism unit with a positive refracting power and alens unit with a positive refracting power so that a mostfield-frame-side surface of the prism unit with a positive refractingpower has a positive refracting power and is configured as an asphericalsurface with a negative refracting power on its periphery.

As mentioned above, when the eyepiece optical system is designed to havethe prism unit, a part of the image erecting means can be shared to theeyepiece optical system, and space can be effectively utilized. When theeyepiece optical system is constructed with the lens unit having apositive refracting power, the diopter can be adjusted in accordancewith the observer's diopter.

In order to reduce the focal length of the eyepiece optical system, itis desirable to increase the positive refracting power of the opticalelement constituting the eyepiece optical system.

However, if the most field-frame-side surface of the eyepiece opticalsystem is configured so that the positive refracting power is increased,and a marginal beam in the proximity of the field frame is renderednearly parallel to the optical axis, the size of the eyepiece opticalsystem in its radial direction will be increased. On the other hand, ifthe most field-frame-side surface of the eyepiece optical system isconfigured so that the positive refracting power is increased, and atthe same time, the size of the eyepiece optical system in its radialdirection is diminished, the angle of inclination will be increased.Consequently, the marginal beam of the first unit at the wide-angleposition is separated from the optical axis, and hence the diameter ofthe first unit must be enlarged.

Thus, when the most field-frame-side surface of the eyepiece opticalsystem has a positive refracting power and is configured as anaspherical surface with a negative refracting power on its periphery,the diameter of the first unit can be diminished. Moreover, correctionfor aberration, notably for distortion, is favorably compatible with apupil combination of the objective optical system and the eyepieceoptical system, notably in an off-axis.

In the real image mode finder optical system of the present invention,it is favorable that the negative refracting power on the periphery ofthe most field-frame-side surface of the prism unit with a positiverefracting power satisfies the following condition:

 −0.7(1/mm)<φ(mh/2)<0(1/mm)  (8)

where φ(mh/2) is a refracting power at a height mh/2 in a directionnormal to the optical axis of the aspherical surface.

As described above, when Condition (8) is satisfied, the negativerefracting power on the periphery of the most field-frame-side surfaceof the positive prism unit can be optimized.

Also, a refracting power φ(y) at a height y of the aspherical surface isobtained as follows. When z is taken as the coordinate in the directionof the optical axis, y is taken as the coordinate normal to the opticalaxis, r denotes the radius of curvature, K denotes a conic constant, andA₄, A₆, A₈, and A₁₀ denote aspherical coefficients, the configuration ofthe aspherical surface is expressed by the following equation:z=(y ² /r)/[1+√{square root over ({1−(1+K)(y/r) ² })}{square root over({1−(1+K)(y/r) ² })}]+ A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ A ₁₀ y ¹⁰

Also, first-order differential dz/dy and second-order differentiald²z/dy² are given from the following formulas:dz/dy=(y/r)/[√{square root over ({1−(1+K)(y/r)²})}{square root over({1−(1+K)(y/r)²})}]+4A ₄ y ³+6A ₆ y ⁵+8A ₈ y ⁷+10A ₁₀ y ¹⁰d ² z/dy ²=(1/r)/[{1−(1+K)(y/r)²}^(3/2)]+12A ₄ y ²+30A ₆ y ⁴+56A ₈ y⁶+90A ₁₀ y ⁸

In this case, the refracting power φ(y) at the height y of theaspherical surface is obtained from the following formula:φ(y)=(n ₂ −n ₁)/r _(asp)where n₁ is the refractive index of the aspherical surface on the objectside thereof and n₂ is the refractive index on the image side.

Also, r_(asp) is defined asr _(asp)=[{1+(dz/dy)²}^(3/2)]/(d ² z/dy ²)

It is favorable that the real image mode finder optical system of thepresent invention is constructed so that the objective optical systemhas at least two lens units, the focal length of the objective opticalsystem is variable, and when the magnification is changed, the at leasttwo lens units are moved along different paths.

When the objective optical system is constructed so that its focallength can be changed, a constant angle of emergence can be obtained,without changing the size of the field frame, even when themagnification is changed.

When the angle of emergence is increased, the phenomenon of a so-calleddiopter shift will occur if the back focal position is shifted. However,when at least two lens units are moved along different paths to changethe magnification, the back focal position of the objective opticalsystem can be kept to be nearly constant.

It is favorable that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a front unitwith a negative refracting power and a rear unit with a positiverefracting power. The front unit is constructed with a plurality of lensunits so that the magnification is changed, ranging from the wide-angleposition to the telephoto position, by moving at least two of theplurality of lens units. The rear unit is constructed with a pluralityof prism units with positive refracting powers so that at least one ofsurfaces opposite to one another, of the plurality of prism units isconfigured to be convex.

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power. The fourth unit iscomprised of a fourth front sub-unit with a positive refracting powerand a fourth rear sub-unit with a positive refracting power, and themagnification is changed, ranging from the wide-angle position to thetelephoto position, by moving the second unit and the third unit. Eachof the first, second, and third units is constructed with a lens, andeach of the fourth front and rear sub-units is constructed with a prismso that at least one of surfaces opposite to each other, of the fourthfront and rear sub-units is configured to be convex.

In the above construction, the real image mode finder optical system issuch that the fourth front sub-unit is comprised of a single prism andhas a single reflecting surface.

In order to increase the angle of emergence, it is only necessary toincrease the size of an image obtained by the objective optical system,that is, the size of the field frame, or to reduce the focal length ofthe eyepiece optical system. However, if the field frame is enlargedwith respect to the focal length of the eyepiece optical system, theobjective optical system must be also enlarged. Moreover, since theburden of correction for aberration to the eyepiece optical system willbe increased, it becomes difficult that good performance of the eyepieceoptical system and compactness due to a simple arrangement arecompatible with each other. Thus, in order to keep the size of thefinder compact and increase the angle of emergence, it is desirable toreduce the focal length of the eyepiece optical system.

However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed, so that the reflecting surface to be placedis limited to one. Consequently, it is necessary that the back focaldistance of the objective optical system is increased to place the imageerecting means there.

Thus, in the present invention, the objective optical system is designedto have, in order to the object side, a front unit with a negativerefracting power, including a plurality of lens units and changing themagnification by moving at least two lens units thereof and a rear unitwith a positive refracting power comprised of a plurality of prism unitswith positive refracting powers.

As mentioned above, when the objective optical system is designed to beof a retrofocus type, the back focal distance of the objective opticalsystem can be increased. Moreover, when the rear unit with a positiverefracting power is constructed with the prism units, the image erectingmeans can be shared. Thus, according to the present invention, the focallength of the eyepiece optical system can be reduced, and a real imagemode finder optical system which has a large angle of emergence and iscompact in design can be achieved.

In the case where the variable magnification ratio of the finder opticalsystem is increased to particularly extend the variable magnificationrange to the wide-angle side, a high refracting power is required forthe rear unit with a positive refracting power. The inclination of themarginal beam with respect to the optical axis where the magnificationis changed at the wide-angle position is large immediately after thebeam emerges from the front unit with a negative refracting power.Hence, in order to make this inclined beam parallel in the proximity ofthe field frame, a great positive refracting power is required on therear side of the front unit with a negative refracting power. In thiscase, it is desirable that the great positive refracting power is sharedamong a plurality of surfaces because the performance of the objectiveoptical system is improved.

The rear unit with a positive refracting power comprised of a pluralityof prism units with positive refracting powers is placed on the eyepieceside of the front unit with a negative refracting power, and at leastone of surfaces opposite to one another, of the plurality of prism unitswith positive refracting powers is configured to be convex. By doing so,the positive refracting power can be shared to the entrance or exitsurface of each of the plurality of prism units with positive refractingpowers, and thus the performance of the objective optical system can beimproved.

When the magnification is changed by moving at least two lens units, thevariable magnification function and the diopter correcting functioninvolved in the magnification change can be exercised.

When the angle of emergence is increased, the diopter shift is liable tooccur. However, by moving at least two lens units of the front unit, thediopter shift involved in the magnification change can be corrected.

As mentioned above, in order to increase the angle of emergence, it isonly necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed, so that the reflecting surface to be placedis limited to one. Consequently, it is necessary that the back focaldistance of the objective optical system is increased to place the imageerecting means there.

Thus, in the present invention, the objective optical system is designedto have, in order to the object side, the first unit with a negativerefracting power, the second unit with a positive refracting power, thethird unit with a negative refracting power, and the fourth unit with apositive refracting power so that the fourth unit includes the fourthfront sub-unit with a positive refracting power and the fourth rearsub-unit with a positive refracting power.

As described above, when the positive refracting power is imparted toeach of the fourth front sub-unit and the fourth rear sub-unit, the backfocal distance of the objective optical system can be increased.Moreover, when the fourth front and rear subunits are constructed withprisms, the function of the image erecting means can be shared. Thus,according to the present invention, the focal length of the eyepieceoptical system can be reduced, and a real image mode finder opticalsystem which has a large angle of emergence and is compact in design canbe obtained.

In the case where In the case where the variable magnification ratio ofthe finder optical system is increased to particularly extend thevariable magnification range to the wide-angle side, high refractingpowers are required for the units with positive refracting powers on theeyepiece side of the third unit. The inclination of the marginal beamwith respect to the optical axis where the magnification is changed atthe wide-angle position is large immediately after the beam emerges fromthe front unit with a negative refracting power. Hence, in order to makethis inclined beam parallel in the proximity of the field frame, a greatpositive refracting power is required on the rear side of the front unitwith a negative refracting power. In this case, it is desirable that thegreat positive refracting power is shared among a plurality of surfacesbecause the performance of the objective optical system is improved.

When the prism units of the fourth front and rear sub-units with twopositive refracting powers are arranged on the eyepiece side of thethird unit and at least one of opposite surfaces of the fourth front andrear sub-units is configured to be convex, the positive refracting powercan be shared to at least one of opposite surfaces of the fourth frontand rear sub-units, and hence the performance of the objective opticalsystem can be improved.

When the magnification is changed by moving at least two units, thevariable magnification function and the diopter correcting functioninvolved in the magnification change can be exercised.

When the angle of emergence is increased, the diopter shift is liable tooccur. However, by moving the second and third units, the diopter shiftinvolved in the magnification change can be corrected.

In order that the thickness of a camera is reduced to provide a compactcamera, it is desirable that a position where the most object-sideoptical axis of the image erecting means, that is, the position of areflecting surface, is brought close to the object side. When themagnification is changed, the image erecting means remains fixed andthereby the arrangement of the finder is simplified. Thus, it isdesirable that the fourth front sub-unit with a positive refractingpower has a reflecting surface.

On the other hand, in order to increase the back focal distance of theobjective optical system, it is desired that most of the reflectingsurfaces having positive refracting powers shared between the fourthfront and rear sub-units are arranged together at a distance away fromthe field frame.

When the objective optical system is constructed so that the fourthfront sub-unit has a single reflecting surface as mentioned above, theopposite surfaces of the fourth front and rear sub-units can be arrangedalong the length of the fourth front sub-unit including one reflectingsurface. Consequently, compactness of the camera and the back focaldistance of the objective optical system can be ensured.

In the real image mode finder optical system of the present invention,it is favorable that the fourth rear sub-unit is constructed with asingle prism and has two reflecting surfaces.

At least four reflecting surfaces are required for the image erectingmeans, and thus if the image erecting means is constructed with fourreflecting surfaces, space efficiency can be improved. In this case,when three of four reflecting surfaces constituting the image erectingmeans are placed in the objective optical system, the burden of a spacefor placing the image erecting means to the eyepiece optical system islessened, and the number of optical elements constituting the eyepieceoptical system can be reduced.

It is favorable that the real image mode finder optical system of thepresent invention satisfies the following condition:−1.0<MG45<−0.5  (9)where MG45 is a combined imaging magnification of the fourth frontsub-unit and a fourth rear sub-unit at an object distance of 3 m.

When Condition (9) is satisfied, the balance between performance andsize of the objective optical system can be held. Below the lower limitof Condition (9), a combined refracting power of the first, second, andthird units must be increased, and thus the fluctuation of aberrationbecomes heavy by movement of the second and third units for changing themagnification. On the other hand, beyond the upper limit of Condition(9), a combined refracting power of the first, second, and third unitsmust be reduced, and thus the diameter of the first unit will beparticularly enlarged.

When the magnification is changed over the range from the wide-angleposition to the telephoto position, it is favorable that the real imagemode finder optical system satisfies the following condition:−1.2<β3<−0.8  (10)where β3 is the imaging magnification of the third unit in a state wherethe imaging magnification of the second unit is −1× at an objectdistance of 3 m.

The second and third units bear the variable magnification function andthe diopter correcting function, but if the diopter correction is notcompletely made, the diopter shift will be produced. In particular, whenthe angle of emergence is increased, the diopter shift is liable tooccur.

When the finder optical system is designed to satisfy Condition (10), astate where the imaging magnification of the second unit is −1× at anobject distance of 3 m practically coincides with a state where theimaging magnification of the third unit is −1× at an object distance of3 m when the magnification is changed over the range from the wide-angleposition to the telephoto position. As a result, diopter correction canbe favorably made over the whole range in which the magnification ischanged.

In the real image mode finder optical system of the present invention,it is favorable that the second unit is constructed with a single lensand satisfies the following condition:−0.6<SF2<0.6  (11)where SF2=(r3+r4)/(r3−r4), which is the shape factor of the second unit,r3 is the radius of curvature of the object-side surface of the secondunit, and r4 is the radius of curvature of the eyepiece-side surface ofthe second unit.

When the finder optical system is designed to satisfy Condition (11),the fluctuation of performance where the magnification is changed can besuppressed. If the upper or lower limit of Condition (11) is passed, thefluctuation of aberration where the magnification is changed becomesheavy.

In the real image mode finder optical system of the present invention,it is desirable that each of the second and third units is constructedwith a single lens and satisfies the following condition:−1.9<f2/f3<−1.0  (12)where f2 is the focal length of the second unit and f3 is the focallength of the third unit.

Condition (12) defines a condition relative to the refracting powers ofthe second and third units for suppressing a change in performance wherethe magnification is changed. Below the lower limit of Condition (12),the refracting power of the third unit is increased, and the fluctuationof aberration where the magnification is changed becomes heavy. Beyondthe upper limit of Condition (12), the refracting power of the secondunit is increased, and the fluctuation of aberration where themagnification is changed becomes heavy.

It is favorable that the real image mode finder optical system of thepresent invention satisfies the following conditions at the same time:−1.0<fw/fFw<−0.4  (13)−1.0−fT/fFT<−0.4  (14)where fFw is a combined focal length of the front unit with a negativerefracting power at the wide-angle position, fFT is a combined focallength of the front unit with a negative refracting power at thetelephoto position, fw is the focal length of the objective opticalsystem at the wide-angle position, and fT is the focal length of theobjective optical system at the telephoto position.

When Conditions (13) and (14) are satisfied at the same time, thebalance between the performance and the back focal distance of theobjective optical system can be maintained. If the lower limit ofCondition (13) or (14) is passed, a negative combined refracting powerof the front unit will be strengthened, and thus the fluctuation ofaberration caused by the movement of the second and third units forchanging the magnification becomes heavy.

On the other hand, if the upper limit of Condition (13) or (14) isexceeded, the negative combined refracting power of the front unit willbe diminished, and hence a long back focal distance caused by theretrofocus arrangement will cease to be completely obtainable.

It is desirable that the real image mode finder optical system of thepresent invention satisfies the following condition:2.7<mT/mW<7.0  (15)where mW is the finder magnification of the entire system at thewide-angle position and mT is the finder magnification of the entiresystem at the telephoto position.

The present invention provides a preferred zoom ratio in the real imagemode finder optical system described above.

Below the lower limit of Condition (15), the performance of the finderoptical system cannot be completely exercised. On the other hand, beyondthe upper limit of Condition (15), the refracting power of each unitbecomes too strong and aberration is liable to occur.

It is favorable that that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the presentinvention includes, in order from the object side, an objective opticalsystem which has a positive refracting power and changes themagnification of the finder, a field frame located in the proximity ofthe imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power. The real image modefinder optical system has an image erecting means, and the objectiveoptical system includes, in order from the object side, a first unitwith a negative refracting power, a second unit with a positiverefracting power, a third unit with a negative refracting power, and afourth unit with a positive refracting power. The magnification ischanged, ranging from the wide-angle position to the telephoto position,by simply moving the second unit toward the object side and the thirdunit toward the eyepiece side. A combined focal length of the first,second, and third units is negative, and when the magnification ischanged over the range from the wide-angle position to the telephotoposition, a combined imaging magnification of the second and third unitsis 1×.

In this case, it is favorable that the real image mode finder opticalsystem constructed as mentioned above satisfies Condition (10).

Furthermore, in the real image mode finder optical system of the presentinvention, it is favorable that the second unit is constructed with asingle lens and satisfies Condition (11).

As described above, in order to increase the angle of emergence, it isonly necessary to increase the size of an image obtained by theobjective optical system, that is, the size of the field frame, or toreduce the focal length of the eyepiece optical system. However, if thefield frame is enlarged with respect to the focal length of the eyepieceoptical system, the objective optical system must be also enlarged.Moreover, since the burden of correction for aberration to the eyepieceoptical system will be increased, it becomes difficult that goodperformance of the eyepiece optical system and compactness due to asimple arrangement are compatible with each other. Thus, in order tokeep the size of the finder compact and increase the angle of emergence,it is desirable to reduce the focal length of the eyepiece opticalsystem.

However, when the focal length of the eyepiece optical system isreduced, the distance on the optical axis between the front principalpoint of the eyepiece optical system and the field frame is diminished,and, for example, space for arranging the optical elements of the imageerecting means is narrowed. Consequently, it is necessary that the backfocal distance of the objective optical system is increased to place theimage erecting means there.

Thus, in the present invention, the objective optical system is designedto have, in order to the object side, the first unit with a negativerefracting power, the second unit with a positive refracting power, thethird unit with a negative refracting power, and the fourth unit with apositive refracting power so that the combined focal length of thefirst, second, and third units is negative.

By doing so, the objective optical system is arranged to be of aretrofocus type, and therefore, the back focal distance of the objectiveoptical system can be increased. Thus, according to the presentinvention, the focal length of the eyepiece optical system can bereduced, and a real image mode finder optical system which has a largeangle of emergence and is compact in design can be achieved.

When the magnification of the finder is changed, it is necessary that avariable magnification function is chiefly imparted to one of at leasttwo moving lens units and a diopter correcting function involved in themagnification change is chiefly imparted to the other. In this case, theamount of movement of the lens unit having the variable magnificationfunction becomes larger than that of the lens unit having the dioptercorrecting function, and a mechanism for movement is liable to becomplicated and oversized.

Thus, in the present invention, the finder optical system is constructedso that the magnification is changed, ranging from the wide-angleposition to the telephoto position, by simply moving the second unittoward the object side and the third unit toward the eyepiece side.

By doing so, both the variable magnification function and the dioptercorrecting function can be shared between the second unit and the thirdunit. Hence, the amount of movement of each of the second and thirdunits where the magnification is change can be kept to a minimum, andcompactness of the mechanism for movement is obtained.

In order to achieve compactness of the objective optical system, it isonly necessary to increase the refracting power of each of the secondand third units for changing the magnification. In this case, however,the fluctuation of aberration where the magnification is changed becomesheavy.

Here, in the whole range in which the magnification is changed, if anattempt is made so that the combined imaging magnification of the secondand third units becomes lower than 1×, there is a tendency that therefracting power of the third unit is increased. In this case, since therefracting power of the first unit must be diminished, the diameter ofthe first unit must be increased.

On the other hand, if an attempt is made so that the combined imagingmagnification of the second and third units becomes higher than 1×,there is a tendency that the refracting power of the second unit isincreased. In this case, since the refracting power of the first unitmust be increased, the diopter shift caused by a change of space betweenthe first and second units becomes particularly considerable.

Thus, if the combined imaging magnification of the second and thirdunits is changed so that it becomes 1×, the balance between theperformance and the size of the objective optical system can beoptimized.

The second and third units bear the variable magnification function andthe diopter correcting function, but if the diopter correction is notcompletely made, the diopter shift will be produced. In particular, whenthe angle of emergence is increased, the diopter shift is liable tooccur.

When the finder optical system is designed to satisfy Condition (10), astate where the imaging magnification of the second unit is −1× at anobject distance of 3 m practically coincides with a state where theimaging magnification of the third unit is −1× at an object distance of3 m when the magnification is changed over the range from the wide-angleposition to the telephoto position. As a result, diopter correction canbe favorably made over the whole range in which the magnification ischanged.

When the finder optical system is designed to satisfy Condition (11),the fluctuation of performance where the magnification is changed can besuppressed. If the upper or lower limit of Condition (11) is passed, thefluctuation of aberration where the magnification is changed becomesheavy.

In the real image mode finder optical system of the present invention,it is favorable that each of the second and third units is constructedwith a single lens and satisfies Condition (12).

Condition (12) defines a condition relative to the refracting powers ofthe second and third units for suppressing a change in performance wherethe magnification is changed. Below the lower limit of Condition (12),the refracting power of the third unit is increased, and the fluctuationof aberration where the magnification is changed becomes heavy. Beyondthe upper limit of Condition (12), the refracting power of the secondunit is increased, and the fluctuation of aberration where themagnification is changed becomes heavy.

It is favorable that the real image mode finder optical system of thepresent invention satisfies the following conditions at the same time:−1.0<fw/fw123<−0.4  (16)−1.0<fr/fr123<−0.4  (17)where fw123 is a combined focal length of the first, second, and thirdunits at the wide-angle position and fT123 is a combined focal length ofthe first, second, and third units at the telephoto position.

When Conditions (16) and (17) are satisfied at the same time, thebalance between the performance and the back focal distance of theobjective optical system can be maintained. If the lower limit ofCondition (16) or (17) is passed, a negative combined refracting powerof each of the first, second, and third units will be strengthened, andthus the fluctuation of aberration caused by the movement of the secondand third units for changing the magnification becomes heavy.

On the other hand, if the upper limit of Condition (16) or (17) isexceeded, the negative combined refracting power of each of the first,second, and third units will be diminished, and hence a long back focaldistance caused by the retrofocus arrangement will cease to becompletely obtainable.

It is favorable that the real image mode finder optical system isconstructed so that when the magnification is changed over the rangefrom the wide-angle position to the telephoto position, the fourth unitremains fixed.

By doing so, the number of units to be moved can be lessened, and costcan be reduced accordingly.

In the real image mode finder optical system of the present invention,it is favorable that the fourth unit is constructed with two opticalunits with positive refracting powers.

In the case where the variable magnification ratio of the finder opticalsystem is increased to particularly extend the variable magnificationrange to the wide-angle side, a high refracting power is required forthe unit with a positive refracting power on the eyepiece side of thethird unit. The inclination of the marginal beam with respect to theoptical axis where the magnification is changed at the wide-angleposition is large immediately after the beam emerges from the thirdunit. Hence, in order to make this inclined beam parallel in theproximity of the field frame, a great positive refracting power isrequired on the rear side of the third unit. In this case, it isdesirable that the great positive refracting power is shared among aplurality of surfaces because the performance of the objective opticalsystem is improved.

As explained above, when the two optical units with positive refractingpowers are arranged on the eyepiece side of the third unit, the lensfunction can be shared between opposite surfaces of the two opticalunits with positive refracting powers, and hence the performance of theobjective optical system can be improved.

In the real image mode finder optical system of the present invention,it is favorable that the fourth unit has a plurality of reflectingsurfaces.

Thus, when at least half of the image erecting function is shared to theobjective optical system, an increase in thickness along the opticalaxis of incidence of the objective optical system can be suppressed andat the same time, the distance between an intermediate image and aneyepiece is reduced. Consequently, a finder which has a large angle ofemergence can be obtained.

In the real image mode finder optical system of the present invention,it is favorable that the two optical units are prisms having reflectingsurfaces.

When at least half of the image erecting function is shared to theobjective optical system, an increase in thickness along the opticalaxis of incidence of the objective optical system can be suppressed andat the same time, the distance between an intermediate image and aneyepiece is reduced. Consequently, a finder which has a large angle ofemergence can be obtained.

It is favorable that the real image mode finder optical system isconstructed so that the magnification is changed, ranging from thewide-angle position to the telephoto position, by moving the first unitas well.

The second and third units bear the variable magnification function andthe diopter correcting function, but if the diopter correction is notcompletely made, the diopter shift will be produced.

Where the units for changing the magnification are constructed with onlythe second and third units, diopter correction cannot be favorably madeover the whole range in which the magnification is changed, unless astate where the imaging magnification of the second unit is −1×practically coincides with a state where the imaging magnification ofthe third unit is −1× when the magnification is changed over the rangefrom the wide-angle position to the telephoto position.

However, when the first unit is also moved to change the magnification,restrictions on imaging magnifications of the second and third units areeliminated, and the performance of the objective optical system can beeasily improved.

The real image mode finder optical system of the present invention maybe constructed so that when the magnification is changed over the rangefrom the wide-angle position to the telephoto position, the first unitremains fixed.

By doing so, the number of units to be moved can be lessened, and costcan be reduced accordingly.

In this case, it is favorable that the real image mode finder opticalsystem of the present invention satisfies Condition (15).

The present invention provides a preferred zoom ratio in the real imagemode finder optical system described above.

Below the lower limit of Condition (15), the performance of the finderoptical system cannot be completely exercised. On the other hand, beyondthe upper limit of Condition (15), the refracting power of each unitbecomes too strong and aberration is liable to occur.

It is favorable that that the photographing apparatus according to thepresent invention has the photographing optical system and the realimage mode finder optical system which has been described.

Also, in the above description, where the reflecting surface isconfigured as a roof reflecting surface, it is assumed that the roofreflecting surface is constructed with two reflecting surfaces.

In accordance with the drawings and numerical data, the embodiments ofthe real image mode finder optical system of the present invention willbe explained below.

In any of the embodiments, the real image mode finder optical systemincludes, in order from the object side, an objective optical systemwith a positive refracting power, a field frame placed in the proximityof the imaging position of the objective optical system, and an eyepieceoptical system with a positive refracting power, and has an imageerecting means.

First Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 1-3 and 5A-5C, the objective optical system includes, inorder from the object side, a first unit G1 with a negative refractingpower, a second unit G2 with a positive refracting power, a third unitG3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a prism P and a positivelens E1 and has a positive refracting power as a whole. Also, in FIG.5A, symbol EP represents an eyepoint.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the first embodiment, anintermediate image formed by the objective optical system is interposedbetween the prism P2 and the prism P, and the field frame, such as thatshown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

The prisms P1 and P2 and the prism P, as shown in FIGS. 1-3, areprovided with reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁ along theoptical path so that the optical axis is bent to erect an image.Specifically, as shown in FIG. 3, the reflecting surface P1 ₁ providedin the prism P1 bends the optical axis in a Y-Z plane; as shown in FIGS.2 and 3, the two reflecting surfaces P2 ₁ and P2 ₂ provided in the prismP2 bend the optical axis in the Y-Z plane and an X-Z plane in this orderfrom the object side; and as shown in FIG. 2, the reflecting surface P₁provided in the prism P bends the optical axis in the X-Z plane. In thisway, an erect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangles of the optical axis bent by the reflecting surfaces P1 ₁ and P₁of the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the reflecting surfaces P2 ₁ and P2 ₂of the prism P2 are larger than 90 degrees. The reflecting surfaces P1 ₁and P₁ of the prism P1 and the prism P are coated with metal films, suchas silver and aluminum. The reflecting surfaces P2 ₁ and P2 ₂ of theprism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface P2 ₂ of theprism P2 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface P₁ of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Also, aberration characteristics in the first embodiment are shown inFIGS. 6A-6D, 7A-7D, and 8A-8D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the first embodiment areshown below. In the numerical data of the first embodiment, m denotes afinder magnification; ω denotes a field angle; f denotes the focallength of the objective optical system; r₁, r₂, . . . represent radii ofcurvature of the surfaces of individual lenses or prisms; d₁, d₂, . . .represent thicknesses of individual lenses or prisms or spacestherebetween; n_(d1), n_(d2), . . . represent refractive indices ofindividual lenses or prisms; and ν_(d1), ν_(d2), . . . represent Abbe'snumbers of individual lenses or prisms; mh represents the maximum widthof the field frame; fe represents the focal length of the eyepieceoptical system; f123 represents a combined focal length of the first tothird units; m23 represents a combined imaging magnification of thesecond and third units where an object distance is 3 m; m2 represents animaging magnification of the second unit at the middle position

The image erecting means includes the prism P1 and the prism P. In thereal image mode finder optical system of the second embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P1 and the prism, P, and the field frame, such as thatshown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is charged in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 have finite curvatures. The entrance surface andthe exit surface of the prism P also have finite curvatures.

The prism P1 and the prism P are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with three reflectingsurfaces (for bending the optical axis twice in the Y-Z plane and oncein the X-Z plane in this order from the object side) and the prism P isprovided with one reflecting surface (for bending the optical axis inthe X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withoptical axis bent by one reflecting surfaces are such that, for example,the angle of the optical axis bent by one reflecting surface of theprism P1 is smaller than 90 degrees and the angles of the optical axisbent by the remaining two reflecting surfaces are larger than 90degrees, while the angle of the optical axis bent by the reflectingsurface of the prism P is smaller than 90 degrees. The reflectingsurfaces making angles smaller the 90 are coated with metal films, suchas silver and aluminum. The reflecting surfaces of angles larger the 90degrees utilize total reflection. However, the angles of the opticalaxis where the object distance is 3 m; and m3 represents an imagingmagnification of the third unit at the middle position where the objectdistance is 3 m.

Also, the configuration of the aspherical surface, as already described,is expressed by the following equation:z=(y ² /r)/[1+√{square root over ({1−(1+K)(y/r) ² })}{square root over({1−(1+K)(y/r) ² })}]+ A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y ¹⁰

These symbols are also applied to the embodiments to be described later.

Numerical data 1 Wide-angle position Middle position Telephoto positionm  0.536  1.016  2.075 ω (°) 33.541 17.525  8.746 f (mm)  8.047 15.25331.147 Pupil dia. (mm)  4.000 r₁ = 83.6172 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.0913 (aspherical) d₂ = D2 (variable) r₃ = 10.3392(aspherical) d₃ = 4.3149 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −21.0217(aspherical) d₄ = D2 (variable) r₅ = −10.0239 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3239 (aspherical) d₆ = D6(variable) r₇ = 11.2869 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.2085 (aspherical) d₈ = 0.5000 r₉ = 15.7633 (aspherical) d₉ = 22.5495n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2605 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.9503 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −38.8890 d₁₃ = 1.7500 r₁₄ = 25.2612 d₁₄ =5.3200 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.9795 (aspherical) d₁₅= 17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2950 A₄ = 2.10279 × 10⁻⁶ A₆ = −2.71836 × 10⁻⁷ A₈ = 1.45499 × 10⁻⁹Third surface K = −0.2610 A₄ = −9.12395 × 10⁻⁵ A₆ = −3.93632 × 10⁻⁷ A₈ =−6.31136 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 8.97235 × 10⁻⁵ A₆ =−4.73271 × 10⁻⁷ A₈ = −1.37810 × 10⁻⁹ Fifth surface K = 0.2143 A₄ =6.18253 × 10⁻⁴ A₆ = −3.45137 × 10⁻⁵ A₈ = 7.99836 × 10⁻⁷ Sixth surface K= −0.0423 A₄ = 1.66996 × 10⁻⁶ A₆ = −2.60860 × 10⁻⁵ A₈ = 6.01778 × 10⁻⁷Eighth surface K = 0.1568 A₄ = 2.22420 × 10⁻⁴ A₆ = −1.28141 × 10⁻⁶ A₈ =3.95727 × 10⁻⁸ Ninth surface K = 0.0140 A₄ = −1.11940 × 10⁻⁵ A₆ =−1.42736 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 4.29178 × 10⁻⁵ A₆ =1.34232 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.6242    7.1879    3.4246 D4    1.2500    8.2976  16.2705 D6    7.8209    5.2097    1.0000 mh = 10.139 mm f123 −10.436−19.857 −41.578 m23    0.529    1.000    2.044 m2  −1.000 m3  −1.000Condition (9) MG45 − 0.773  −0.775  −0.776 Conditions (1), (7) mh/fe =0.676 Conditions (2), (3) fe = 15.009 mm Condition (8) φ (mh/2) =−0.377955 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.341Condition (12) f2/f3 = −1.619 Condition (13) fw/fFw = −0.771 Condition(14) fT/fFT = −0.749 Condition (15) mT/mW = 3.871 Condition (16)fw/fw123 = −0.771 Condition (17) fT/fT123 = −0.749

Second Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 9A-9C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with a positive lens L and the prismP1. The eyepiece optical system is constructed with a prism P and apositive lens E1 and has a positive refracting power as a whole. bent bythe reflecting surfaces are not limited to the above description. Forexample, the angle of the optical axis bent by the most field-frame-sidereflecting surface of the prism P1 may be made smaller than 90 degreesso that this reflecting surface is coated with a metal film. Moreover,the angle of the optical axis bent by the reflecting surface of theprism P may be made larger than 90 degrees so that this reflectingsurface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with and observer's diopter.

Also, aberration characteristics is the second embodiment are shown inFIGS. 10A-10D, 11A-11D, and 12A-12D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the second embodiment areshown below.

Numerical data 2 Wide-angle position Middle position Telephoto positionm  0.685  1.176  2.016 ω (°) 26.680 15.434  8.985 f (mm) 10.290 17.64930.256 Pupil dia. (mm)  4.000 r₁ = 37.0457 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 9.2320 (aspherical) d₂ = D2 (variable) r₃ = 9.5256(aspherical) d₃ = 4.4760 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −22.0049d₄ = D4 (variable) r₅ = −10.2911 d₅ = 0.7000 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 9.8912 (aspherical) d₆ = D6 (variable) r₇ = 36.5176 d₇ =3.5263 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −11.2570 (aspherical) d₈ =0.5000 r₉ = 17.5358 d₉ = 29.0967 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−218.6484 d₁₀ = 2.7527 r₁₁ = ∞ (field frame) d₁₁ = 2.9177 r₁₂ = 19.1732(aspherical) d₁₂ = 17.0445 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ =−20.5269 d₁₃ = 1.4765 r₁₄ = 39.9369 (aspherical) d₁₄ = 3.4455 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −20.1555 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3017 A₄ =4.40512 × 10⁻⁵ A₆ = 1.04845 × 10⁻⁶ A₈ = −4.86973 × 10⁻⁹ Third surface K= −0.1847 A₄ = −1.74316 × 10⁻⁴ A₆ = −2.38197 × 10⁻⁷ A₈ = −6.24988 × 10⁻⁹Sixth surface K = −0.0683 A₄ = −4.82178 × 10⁻⁴ A₆ = 3.96724 × 10⁻⁶ A₈ =−3.64804 × 10⁻⁸ Eighth surface K = 0.1808 A₄ = 9.81681 × 10⁻⁵ A₆ =8.46115 × 10⁻⁷ A₈ = 8.50642 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−5.68528 × 10⁻⁴ A₆ = −1.76882 × 10⁻⁷ Fourteenth surface K = 0.0000 A₄ =−5.49243 × 10⁻⁵ A₆ = 1.22082 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =−2.37429 × 10⁻⁵ A₆ = 1.03731 × 10⁻⁶ Wide-angle position Middle positionTelephoto position Zoom data D2 11.6070 8.0586  4.1006 D4  1.1067 7.008613.2454 D6  6.3793 4.0397  1.6737 mh = 9.765 mm Conditions (1), (7)mh/fe = 0.650 Conditions (2), (3) fe = 15.011 mm

Third Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 13A-13C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the realimage mode finder optical system of the third embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along theoptical path so that the optical axis is bent to obtain an erect image.For example, the prism P1 is provided with one reflecting surface (forbending the optical axis in the Y-Z plane) and the prism P2 is providedwith three reflecting surfaces (for bending the optical axis once in theY-Z plane and twice in the X-Z plane in this order from the object side)to erect the image. Also, the arrangement of the reflecting surfaces isbased on that of a Porro prism. Angles made with the optical axis bentby the reflecting surfaces are such that, for example, the angle of theoptical axis bent by the reflecting surface of the prism P1 is smallerthan 90 degrees, while the angles of the optical axis bent by tworeflecting surfaces of the prism P2 are larger than 90 degrees and theangle of the optical axis bent by the remaining one reflecting surfaceis smaller than 90 degrees. The reflecting surfaces making anglessmaller than 90 degrees are coated with metal films, such as silver andaluminum. The reflecting surfaces of angles larger than 90 degreesutilize total reflection. The positive lens E1 is constructed so thatdiopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the third embodiment are shown inFIGS. 14A-14D, 15A-15D, and 16A-16D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the third embodiment areshown below.

Numerical data 3 Wide-angle position Middle position Telephoto positionm  0.692  1.181  2.018 ω (°) 26.656 15.374  8.976 f (mm) 10.375 17.70930.248 Pupil dia. (mm)  4.000 r₁ = −37.0118 d₁ = 1.6264 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 15.0266 (aspherical) d₂ = D2 (variable) r₃ = 13.6624(aspherical) d₃ = 4.2776 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −19.7350d₄ = D4 (variable) r₅ = −23.9768 d₅ = 0.6800 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 15.4052 (aspherical) d₆ = D6 (variable) r₇ = 64.0979 d₇ =14.4273 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −16.0524 (aspherical) d₈ =0.5000 r₉ = 46.4363 d₉ = 39.5267 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−21.0120 d₁₀ = 3.7943 r₁₁ = ∞ (field frame) d₁₁ = 6.9095 r₁₂ = −9.9877(asphrical) d₁₂ = 3.6912 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−15.7572 d₁₃ = 0.9421 r₁₄ = 19.1293 (aspherical) d₁₄ = 7.8836 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −10.9574 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3019 A₄ =−1.08535 × 10⁻⁴ A₆ = 1.48477 × 10⁻⁶ A₈ = −7.37060 × 10⁻⁹ Third surface K= −0.1784 A₄ = −1.38562 × 10⁻⁴ A₆ = 1.91486 ×10⁻⁷ A₈ = −9.59282 × 10⁻¹⁰Sixth surface K = −0.0760 A₄ = −4.70450 × 10⁻⁵ A₆ = −2.11500 × 10⁻⁶ A₈ =3.61544 × 10⁻⁸ Eighth surface K = 0.1930 A₄ = 4.06798 × 10⁻⁵ A₆ =−8.51164 × 10⁻⁸ A₈ = 3.41981 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−4.97284 × 10⁻⁴ A₆ = −5.19125 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄=1.11128 × 10⁻⁴ A₆ = −2.84749 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.70029 × 10⁻⁴ A₆ = −6.56818 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 25.7084 12.8854  7.7602 D4  1.0000 9.0863 19.8650 D6  2.8644  5.0585  1.4948 mh = 9.621 mm Conditions (1),(7) mh/fe = 0.642 Conditions (2), (3) fe = 14.990 mm

Fourth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 17A-17C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the realimage mode finder optical system of the fourth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along theoptical path so that the optical axis is bent to obtain an erect image.For example, the prism P1 is provided with one reflecting surface (forbending the optical axis in the Y-Z plane) and the prism P2 is providedwith three reflecting surfaces (for bending the optical axis once in theY-Z plane and twice in the X-Z plane in this order from the object side)to erect the image. Also, the arrangement of the reflecting surfaces isbased on that of a Porro prism. Angles made with the optical axis bentby the reflecting surfaces are such that, for example, the angle of theoptical axis bent by the reflecting surface of the prism P1 is smallerthan 90 degrees, while the angles of the optical axis bent by tworeflecting surfaces of the prism P2 are larger than 90 degrees and theangle of the optical axis bent by the remaining one reflecting surfaceis smaller than 90 degrees. The reflecting surfaces making anglessmaller than 90 degrees are coated with metal films, such as silver andaluminum. The reflecting surfaces of angles larger than 90 degreesutilize total reflection. The positive lens E1 is constructed so thatdiopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the fourth embodiment are shown inFIGS. 18A-18D, 19A-19D, and 20A-20D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the fourth embodiment areshown below.

Numerical data 4 Wide-angle position Middle position Telephoto positionm  0.574  0.980  1.680 ω (°) 26.946 15.541  9.003 f (mm)  8.612 14.70625.218 Pupil dia. (mm)  4.000 r₁ = −27.7265 d₁ = 0.7033 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 12.5528 (aspherical) d₂ = D2 (variable) r₃ = 11.3610(aspherical) d₃ = 3.8444 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −15.8341d₄ = D4 (variable) r₅ = −18.1098 d₅ = 0.7000 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 11.6071 (aspherical) d₆ = D6 (variable) r₇ = 53.8289 d₇ =12.8726 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −14.5655 (aspherical) d₈ =1.0000 r₉ = 23.4433 d₉ = 34.8807 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−28.7418 d₁₀ = 1.4329 r₁₁ = ∞ (field frame) d₁₁ = 6.9526 r₁₂ = −12.6182(aspherical) d₁₂ = 3.6221 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−15.2579 d₁₃ = 1.1803 r₁₄ = 24.0716 (aspherical) d₁₄ = 8.3376 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −11.3348 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3022 A₄ =−2.00833 × 10⁻⁴ A₆ = 3.41784 × 10⁻⁶ A₈ = −1.63261 × 10⁻⁸ Third surface K= −0.1825 A₄ = −2.54261 × 10⁻⁴ A₆ = 5.60513 × 10⁻⁷ A₈ = −3.79136 × 10⁻⁹Sixth surface K = −0.0762 A₄ = −1.57743 × 10⁻⁴ A₆ = −3.09431 × 10⁻⁶ A₈ =4.76542 × 10⁻⁸ Eighth surface K = 0.1928 A₄ = 4.63808 × 10⁻⁵ A₆ =−2.97595 × 10⁻⁷ A₈ = 8.60163 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−6.08556 × 10⁻⁴ A₆ = −8.85765 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄ =1.52011 × 10⁻⁴ A₆ = −1.19503 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.06106 × 10⁻⁴ A₆ = 8.55846 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 21.4497 10.4751  6.4304 D4  1.0000 7.7777 16.8353 D6  1.9906  3.8269  1.3800 mh = 8.107 mm Conditions (1),(7) mh/fe = 0.540 Conditions (2), (3) fe = 15.010 mm

Fifth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 21A-21C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the realimage mode finder optical system of the fifth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along theoptical path so that the optical axis is bent to obtain an erect image.For example, the prism P1 is provided with one reflecting surface (forbending the optical axis in the Y-Z plane) and the prism P2 is providedwith three reflecting surfaces (for bending the optical axis once in theY-Z plane and twice in the X-Z plane in this order from the object side)to erect the image. Also, the arrangement of the reflecting surfaces isbased on that of a Porro prism. Angles made with the optical axis bentby the reflecting surfaces are such that, for example, the angle of theoptical axis bent by the reflecting surface of the prism P1 is smallerthan 90 degrees, while the angles of the optical axis bent by tworeflecting surfaces of the prism P2 are larger than 90 degrees and theangle of the optical axis bent by the remaining one reflecting surfaceis smaller than 90 degrees. The reflecting surfaces making anglessmaller than 90 degrees are coated with metal films, such as silver andaluminum. The reflecting surfaces of angles larger than 90 degreesutilize total reflection. The positive lens E1 is constructed so thatdiopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the fifth embodiment are shown inFIGS. 22A-22D, 23A-23D, and 24A-24D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the fifth embodiment areshown below.

Numerical data 5 Wide-angle position Middle position Telephoto positionm  0.873  1.293  2.418 ω (°) 24.751 16.220  8.611 f (mm) 13.110 19.40936.290 Pupil dia. (mm)  4.000 r₁ = −39.3543 d₁ = 2.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 20.1886 (aspherical) d₂ = D2 (variable) r₃ = 17.8228(aspherical) d₃ = 4.5550 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −20.6969d₄ = D4 (variable) r₅ = −26.5948 d₅ = 0.9712 n_(d5) = 1.58423 V_(d5) =30.49 r₆ = 21.3842 (aspherical) d₆ = D6 (variable) r₇ = 49.7469 d₇ =16.0933 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −23.8038 (aspherical) d₈ =0.6446 r₉ = 38.3198 d₉ = 43.7612 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−63.9202 d₁₀ = 2.7501 r₁₁ = ∞ (field frame) d₁₁ = 7.1509 r₁₂ = −7.9810(aspherical) d₁₂ = 3.6432 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−11.3215 d₁₃ = 1.2765 r₁₄ = 16.6904 (aspherical) d₁₄ = 7.6344 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −13.2210 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3021 A₄ =−3.80325 × 10⁻⁵ A₆ = 5.97449 × 10⁻⁷ A₈ = −2.67271 × 10⁻⁹ Third surface K= −0.1774 A₄ = −7.61365 × 10⁻⁵ A₆ = 1.22273 × 10⁻⁷ A₈ = −3.41547 × 10⁻¹⁰Sixth surface K = −0.0759 A₄ = −3.60399 × 10⁻⁵ A₆ = −1.18573 × 10⁻⁷ A₈ =9.28811 × 10⁻¹⁰ Eighth surface K = 0.1900 A₄ = 1.33964 × 10⁻⁵ A₆ =5.39206 × 10⁻⁸ A₈ = −9.03386 × 10⁻¹¹ Twelfth surface K = 0.0000 A₄ =−2.69230 × 10⁻⁴ A₆ = −2.03083 × 10⁻⁶ Fourteenth surface K = 0.0000 A₄ =8.14903 × 10⁻⁵ A₆ = −1.34641 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.81061 × 10⁻⁴ A₆ = −6.24901 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 29.0804 15.7590  8.2552 D4  1.0000 8.0891 22.1773 D6  3.1755  8.1368  2.0110 mh = 11.006 mm Conditions(1), (7) mh/fe = 0.733 Conditions (2), (3) fe = 15.010 mm

Sixth Embodiment

The arrangement of this embodiment is similar to that of the firstembodiment described with reference to FIGS. 1-4. FIGS. 25A-25D show thearrangement of the sixth embodiment. In this embodiment, low-dispersionglass is used for the positive lens E1 to suppress chromatic aberrationof magnification produced in the eyepiece optical system.

Also, aberration characteristics in the sixth embodiment are shown inFIGS. 26A-26D, 27A-27D, 28A-28D, and 29A-29D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the sixth embodiment areshown below.

Numerical data 6 Wide-angle position Middle position Telephoto positionm  0.743  1.016  2.072 ω (°) 23.854 17.511  8.739 f (mm) 11.156 15.25231.104 Pupil dia. (mm)  4.000 r₁ = 81.9112 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.0742 (aspherical) d₂ = D2 (variable) r₃ = 10.3535(aspherical) d₃ = 4.3238 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −20.9984(aspherical) d₄ = D4 (variable) r₅ = −10.0333 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3333 (aspherical) d₆ = D6(variable) r₇ = 11.3130 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.1581 (aspherical) d₈ = 0.5000 r₉ = 15.7417 (aspherical) d₉ = 22.5485n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2615 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.2310 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −39.1300 d₁₃ = 1.7500 r₁₄ = 24.5529 d₁₄ =5.3200 n_(d14) = 1.49700 ν_(d14) = 81.54 r₁₅ = −15.8669 (aspherical) d₁₅= 17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2950 A₄ = 5.82582 × 10⁻⁶ A₆ = −2.91852 × 10⁻⁷ A₈ = 1.53866 × 10⁻⁹Third surface K = −0.2618 A₄ = −8.99427 × 10⁻⁵ A₆ = −3.14079 × 10⁻⁷ A₈ =−8.23133 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 8.74333 × 10⁻⁵ A₆ =−3.77249 × 10⁻⁷ A₈ = −3.31925 × 10⁻⁹ Fifth surface K = 0.2138 A₄ =6.11164 × 10⁻⁴ A₆ = −3.28266 × 10⁻⁵ A₈ = 7.55363 × 10⁻⁷ Sixth surface K= −0.0425 A₄ = 2.44411 × 10⁻⁵ A₆ = −2.80434 × 10⁻⁵ A₈ = 6.70880 × 10⁻⁷Eighth surface K = 0.1564 A₄ = 2.36396 × 10⁻⁴ A₆ = −1.54507 × 10⁻⁶ A₈ =3.28513 × 10⁻⁸ Ninth surface K = 0.0138 A₄ = 7.48388 × 10⁻⁶ A₆ =−1.90449 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 5.20019 × 10⁻⁵ A₆ =1.50643 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1623 7.1846  3.4243 D4 4.9049 8.2975 16.2619 D6 6.61905.2041  1.0000 mh = 10.121 mm Conditions (1), (7) mh/fe = 0.674Condition (4) ν = 81.54 Conditions (2), (3) fe = 15.010 mm

Seventh Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 30A-30D, the objective optical system includes, in orderfrom the object side, a first unit G1 with a negative refracting power,a second unit G2 with a positive refracting power, a third unit G3 witha negative refracting power, and a fourth unit G4 with a positiverefracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the seventh embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P2 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures, that is, are configured as lens surfaces. Theentrance surface and the exit surface of the prism P also have finitecurvatures.

The prisms P1 and P2 and the prism P, as in the first embodiment shownin FIGS. 1-3, are provided with the reflecting surfaces along theoptical path so that the optical axis is bent to erect an image. Forexample, one reflecting surface provided in the prism P1 bends theoptical axis in the Y-Z plane; two reflecting surfaces provided in theprism P2 bend the optical axis in the Y-Z plane and the X-Z plane inthis order from the object side; and one reflecting surface provided inthe prism P bends the optical axis in the X-Z plane. In this way, anerect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangles of the optical axis bent by the reflecting surfaces of the prismP1 and the prism P are smaller than 90 degrees and the angles of theoptical axis bent by the two reflecting surfaces of the prism P2 arelarger than 90 degrees. The reflecting surfaces of the prism P1 and theprism P are coated with metal films, such as silver and aluminum. Thetwo reflecting surfaces of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface of the prismP2 may be made smaller than 90 degrees so that this reflecting surfaceis coated with a metal film. Moreover, the angle of the optical axisbent by the reflecting surface of the prism P may also be made largerthan 90 degrees so that this reflecting surface utilizes totalreflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Also, aberration characteristics in the seventh embodiment are shown inFIGS. 31A-31D, 32A-32D, 33A-33D, and 34A-34D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the seventh embodiment areshown below.

Numerical data 7 Wide-angle position Middle position Telephoto positionm  0.743  1.015  2.070 ω (°) 23.875 17.526  8.746 f (mm) 11.146 15.23731.075 Pupil dia. (mm)  4.000 r₁ = 81.9602 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.0611 (aspherical) d₂ = D2 (variable) r₃ = 10.3753(aspherical) d₃ = 4.3253 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −20.8601(aspherical) d₄ = D4 (variable) r₅ = −10.0315 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3315 (aspherical) d₆ = D6 r₇ =11.2984 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −23.0708(aspherical) d₈ = 0.5000 r₉ = 15.8095 (aspherical) d₉ = 22.5530 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2570 r₁₁ = ∞ (field frame) d₁₁ =2.5500 r₁₂ = 15.4188 (aspherical) d₁₂ = 15.5600 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −37.3902 d₁₃ = 1.7500 r₁₄ = 20.4078 d₁₄ = 5.3200n_(d14) = 1.43389 ν_(d14) = 95.15 r₁₅ = −14.4726 (aspherical) d₁₅ =17.0491 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2949 A₄ = 6.66017 × 10⁻⁶ A₆ = −2.62591 × 10⁻⁷ A₈ = 1.12121 × 10⁻⁹Third surface K = −0.2625 A₄ = −7.97190 × 10⁻⁵ A₆ = −6.29748 × 10⁻⁷ A₈ =−1.17464 × 10⁻⁹ Fourth surface K = −0.0226 A₄ = 9.61346 × 10⁻⁵ A₆ =−6.24988 × 10⁻⁷ A₈ = −2.63996 × 10⁻⁹ Fifth surface K = 0.2132 A₄ =6.22361 × 10⁻⁴ A₆ = −3.35122 × 10⁻⁵ A₈ = 7.43683 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = 3.84712 × 10⁻⁵ A₆ = −2.91300 × 10⁻⁵ A₈ = 6.92795 × 10⁻⁷Eighth surface K = 0.1561 A₄ = 2.24263 × 10⁻⁴ A₆ = −1.03011 × 10⁻⁶ A₈ =3.32247 × 10⁻⁸ Ninth surface K = 0.0135 A₄ = −5.19982 × 10 ⁻⁶ A₆ =−1.46612 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 7.35154 × 10⁻⁵ A₆ =2.26014 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1683 7.1925  3.4339 D4 4.8993 8.2891 16.2507 D6 6.61715.2031  1.0000 mh = 10.133 mm Conditions (1), (7) mh/fe = 0.675Condition (4) ν = 95.15 Conditions (2), (3) fe = 15.010 mm

Eighth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 35A-35D, the objective optical system includes, in orderfrom the object side, a first unit G1 with a negative refracting power,a second unit G2 with a positive refracting power, a third unit G3 witha negative refracting power, and a fourth unit G4 with a positiverefracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with a cemented lens component CEcomprised of a positive lens element CE1 and a negative lens element CE2and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the eighth embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P2 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

The prisms P1 and P2 and the prism P are provided with the reflectingsurfaces along the optical path so that the optical axis is bent toerect an image. For example, the prism P1 is provided with onereflecting surface (for bending the optical axis in the Y-Z plane), theprism P2 is provided with two reflecting surfaces (for bending theoptical axis in the Y-Z plane and the X-Z plane), and the prism P isprovided with one reflecting surface (for bending the optical axis inthe X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angles of the optical axis bent by the reflecting surfacesof the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the two reflecting surfaces of theprism P2 are larger than 90 degrees. The reflecting surfaces of theprism P1 and the prism P are coated with metal films, such as silver andaluminum. The two reflecting surfaces of the prism P2 utilize totalreflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface of the prismP2 may be made smaller than 90 degrees so that this reflecting surfaceis coated with a metal film. Moreover, the angle of the optical axisbent by the reflecting surface of the prism P may also be made largerthan 90 degrees so that this reflecting surface utilizes totalreflection.

The cemented lens component CE is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

In the eighth embodiment, the cemented lens component CE including, inorder from the object side, the positive lens element and the negativelens element is used to suppress the chromatic aberration ofmagnification produced in the eyepiece optical system.

Also, aberration characteristics in the eighth embodiment are shown inFIGS. 36A-36D, 37A-37D, 38A-38D, and 39A-39D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the eighth embodiment areshown below.

Numerical data 8 Wide-angle position Middle position Telephoto positionm  0.743  1.020  2.076 ω (°) 23.954 17.549  8.727 f (mm) 11.160 15.30431.158 Pupil dia. (mm)  4.000 r₁ = 75.9203 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.0850 (aspherical) d₂ = D2 (variable) r₃ = 10.2485(aspherical) d₃ = 4.2776 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −21.9093d₄ = D4 (variable) r₅ = −10.0501 (aspherical) d₅ = 1.0000 n_(d5) =1.58425 ν_(d5) = 30.35 r₆ = 10.3501 (aspherical) d₆ = D6 (variable) r₇ =11.5799 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −21.8697(aspherical) d₈ = 0.5000 r₉ = 15.8360 (aspherical) d₉ = 22.6385 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1715 r₁₁ = ∞ (field frame) d₁₁ =2.5500 r₁₂ = 18.8734 (aspherical) d₁₂ = 15.5600 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −20.0934 d₁₃ = 1.7500 r₁₄ = 36.0448 d₁₄ = 5.3393n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −13.2074 d₁₅ = 1.0000 n_(d15) =1.58423 ν_(d15) = 30.49 r₁₆ = −18.5585 (aspherical) d₁₆ = 17.0491 r₁₇ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.2950 A₄ =−2.88906 × 10⁻⁵ A₆ = 1.81910 × 10⁻⁷ A₈ = −1.52765 × 10⁻⁹ Third surface K= −0.2463 A₄ = −1.12182 × 10⁻⁴ A₆ = −6.22353 × 10⁻⁷ A₈ = 2.82153 × 10⁻⁹Fourth surface K = −0.0226 A₄ = 8.40588 × 10⁻⁵ A₆ = −7.72274 × 10⁻⁷ A₈ =6.21797 × 10⁻⁹ Fifth surface K = 0.2122 A₄ = 1.04005 × 10⁻³ A₆ =−6.22976 × 10⁻⁵ A₈ = 1.48889 × 10⁻⁶ Sixth surface K = −0.0428 A₄ =4.20510 × 10⁻⁴ A₆ = −5.35363 × 10⁻⁵ A₈ = 1.24406 × 10⁻⁶ Eighth surface K= 0.1561 A₄ = 2.78620 × 10⁻⁴ A₆ = −1.75114 × 10⁻⁶ A₈ = 1.84964 × 10⁻⁸Ninth surface K = 0.0138 A₄ = 7.75842 × 10⁻⁵ A₆ = −2.54066 × 10⁻⁶Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ = 1.07234 × 10⁻⁵Sixteenth surface K = 0.0000 A₄ = 1.54561 × 10⁻⁵ A₆ = 6.06156 × 10⁻⁸Wide-angle position Middle position Telephoto position Zoom data D29.1388 7.1293  3.3607 D4 4.9642 8.4021 16.3723 D6 6.6307 5.2010  0.9994mh = 10.095 mm Conditions (1), (7) mh/fe = 0.673 Conditions (2), (3) fe= 15.010 mm Conditions (5), (6) νp − νn = 25.29

Ninth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 40A-40D, the objective optical system includes, in orderfrom the object side, a first unit G1 with a negative refracting power,a second unit G2 with a positive refracting power, a third unit G3 witha negative refracting power, and a fourth unit G4 with a positiverefracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the cemented lens componentCE comprised of the positive lens element CE1 and the negative lenselement CE2 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the ninth embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P2 and the prism P, and the field frame,such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by moving the second unit G2 and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havefinite curvatures. The entrance surface and the exit surface of theprism P also have finite curvatures.

The prisms P1 and P2 and the prism P are provided with the reflectingsurfaces along the optical path so that the optical axis is bent toerect an image. For example, the prism P1 is provided with onereflecting surface (for bending the optical axis in the Y-Z plane), theprism P2 is provided with two reflecting surfaces (for bending theoptical axis in the Y-Z plane and the X-Z plane), and the prism P isprovided with one reflecting surface (for bending the optical axis inthe X-Z plane) to erect the image. Also, the arrangement of thereflecting surfaces is based on that of a Porro prism. Angles made withthe optical axis bent by the reflecting surfaces are such that, forexample, the angles of the optical axis bent by the reflecting surfacesof the prism P1 and the prism P are smaller than 90 degrees and theangles of the optical axis bent by the two reflecting surfaces of theprism P2 are larger than 90 degrees. The reflecting surfaces of theprism P1 and the prism P are coated with metal films, such as silver andaluminum. The two reflecting surfaces of the prism P2 utilize totalreflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface of the prismP2 may be made smaller than 90 degrees so that this reflecting surfaceis coated with a metal film. Moreover, the angle of the optical axisbent by the reflecting surface of the prism P may also be made largerthan 90 degrees so that this reflecting surface utilizes totalreflection.

The cemented lens component CE is constructed so that diopter adjustmentcan be made in accordance with an observer's diopter.

In the ninth embodiment, the cemented lens component CE including, inorder from the object side, the positive lens element and the negativelens element is used to suppress the chromatic aberration ofmagnification produced in the eyepiece optical system.

Also, aberration characteristics in the ninth embodiment are shown inFIGS. 41A-41D, 42A-42D, 43A-43D, and 44A-44D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the ninth embodiment areshown below.

Numerical data 9 Wide-angle position Middle position Telephoto positionm  0.745  1.019  2.078 ω (°) 23.864 17.523  8.748 f (mm) 11.179 15.28831.185 Pupil dia. (mm)  4.000 r₁ = 83.1968 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.0574 (aspherical) d₂ = D2 (variable) r₃ = 10.4051(aspherical) d₃ = 4.3247 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −20.6708(aspherical) d₄ = D4 (variable) r₅ = −10.0283 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3283 (aspherical) d₆ = D6(variable) r₇ = 11.0837 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−23.2992 (aspherical) d₈ = 0.5000 r₉ = 16.1348 (aspherical) d₉ = 22.5851n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2249 r₁₁ = ∞ (fieldframe) d₁₁ = 2.5500 r₁₂ = 15.1194 (aspherical) d₁₂ = 15.5600 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −32.9857 d₁₃ = 1.7500 r₁₄ = 22.3114 d₁₄ =1.0000 n_(d14) = 1.58423 ν_(d14) = 30.49 r₁₅ = 13.0456 d₁₅ = 5.4129n_(d15) = 1.52542 ν_(d15) = 55.78 r₁₆ = −18.6581 (aspherical) d₁₆ =17.0491 r₁₇ = ∞ (eyepiece) Aspherical coefficients Second surface K =−1.2945 A₄ = 9.89743 × 10⁻⁶ A₆ = −4.30715 × 10⁻⁷ A₈ = 2.58833 × 10⁻⁹Third surface K = −0.2627 A₄ = −6.69210 × 10⁻⁵ A₆ = −9.19006 × 10⁻⁷ A₈ =6.64337 × 10⁻¹⁰ Fourth surface K = −0.0228 A₄ = 1.06273 × 10⁻⁴ A₆ =−8.28362 × 10⁻⁷ A₈ = 3.85729 × 10⁻⁹ Fifth surface K = 0.2133 A₄ =6.06366 × 10⁻⁴ A₆ = −2.97302 × 10⁻⁵ A₈ = 5.98935 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = 4.82034 × 10⁻⁵ A₆ = −2.89969 × 10⁻⁵ A₈ = 6.72146 × 10⁻⁷Eighth surface K = 0.1560 A₄ = 2.50445 × 10⁻⁴ A₆ = −1.47471 × 10⁻⁶ A₈ =4.11057 × 10⁻⁸ Ninth surface K = 0.0136 A₄ = 5.39717 × 10⁻⁶ A6 =−1.68771 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Sixteenth surface K = 0.0000 A₄ = 3.44659 × 10⁻⁵ A₆ =1.08095 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 9.1868 7.2088  3.4518 D4 4.8856 8.2783 16.2383 D6 6.61295.1982  0.9952 mh = 10.217 mm Conditions (1), (7) mh/fe = 0.681Conditions (2), (3) fe = 15.006 mm Conditions (5), (6) νp − νn = 25.29

Tenth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 45A-45D, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thepositive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the realimage mode finder optical system of the tenth embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along theoptical path so that the optical axis is bent to obtain an erect image.For example, the prism P1 is provided with one reflecting surface (forbending the optical axis in the Y-Z plane) and the prism P2 is providedwith three reflecting surfaces (for bending the optical axis once in theY-Z plane and twice in the X-Z plane in this order from the object side)to erect the image. Also, the arrangement of the reflecting surfaces isbased on that of a Porro prism. Angles made with the optical axis bentby the reflecting surfaces are such that, for example, the angle of theoptical axis bent by the reflecting surface of the prism P1 is smallerthan 90 degrees, while the angles of the optical axis bent by tworeflecting surfaces of the prism P2 are larger than 90 degrees and theangle of the optical axis bent by the remaining one reflecting surfaceis smaller than 90 degrees. The reflecting surfaces making anglessmaller than 90 degrees are coated with metal films, such as silver andaluminum. The reflecting surfaces of angles larger than 90 degreesutilize total reflection. The positive lens E1 is constructed so thatdiopter adjustment can be made in accordance with an observer's diopter.

In the tenth embodiment, low-dispersion glass is used for the positivelens E1 to suppress chromatic aberration of magnification produced inthe eyepiece optical system.

Also, aberration characteristics in the tenth embodiment are shown inFIGS. 46A-46D, 47A-47D, 48A-48D, and 49A-49D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the tenth embodiment areshown below.

Numerical data 10 Wide-angle position Middle position Telephoto positionm  0.686  1.177  2.019 ω (°) 26.700 15.294  8.889 f (mm) 10.290 17.65030.261 Pupil dia. (mm)  4.000 r₁ = −35.4073 d₁ = 1.3547 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 15.7324 (aspherical) d₂ = D2 (variable) r₃ = 14.1173(aspherical) d₃ = 4.2036 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −19.7136d₄ = D4 (variable) r₅ = −21.3268 d₅ = 1.0000 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 15.4585 (aspherical) d₆ = D6 (variable) r₇ = 47.9547 d₇ =14.7087 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −16.9222 (aspherical) d₈ =0.5000 r₉ = 40.5011 d₉ = 39.7256 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−22.4670 d₁₀ = 4.0295 r₁₁ = ∞ (field frame) d₁₁ = 7.6484 r₁₂ = −6.8411(aspherical) d₁₂ = 3.0616 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−9.5101 d₁₃ = 1.9354 r₁₄ = 16.4813 d₁₄ = 5.2395 n_(d14) = 1.49700ν_(d14) = 81.54 r₁₅ = −12.4181 (aspherical) d₁₅ = 15.7651 r₁₆ = ∞(eyepoint) Aspherical coefficients Second surface K = −1.3019 A₄ =−1.03082 × 10⁻⁴ A₆ = 1.18309 × 10⁻⁶ A₈ = −3.69689 × 10⁻⁹ Third surface K= −0.1784 A₄ = −1.31901 × 10⁻⁴ A₆ = 1.62576 × 10⁻⁷ A₈ = −5.25998 × 10⁻¹⁰Sixth surface K = −0.0760 A₄ = −7.29856 × 10⁻⁵ A₆ = −1.57784 × 10⁻⁶ A₈ =2.85950 × 10⁻⁸ Eighth surface K = 0.1940 A₄ = 3.47928 × 10⁻⁵ A₆ =5.46298 × 10⁻⁸ A₈ = 1.40140 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ =−2.29965 × 10⁻⁴ A₆ = −5.49255 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ =1.23613 × 10⁻⁴ A₆ = 7.32239 × 10⁻⁷ Wide-angle position Middle positionTelephoto position Zoom data D2 25.8585 12.8666  7.9000 D4  1.0000 9.3310 20.3050 D6  3.2733  5.0026  1.7063 mh = 9.539 mm Conditions (1),(7) mh/fe = 0.636 Condition (4) ν = 81.54 Conditions (2), (3) fe =14.990 mm

Eleventh Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 50A-50D, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and a fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the negative lens L1 and thecemented lens component CE comprised of the negative lens element CE 2and the positive lens element CE1, and has a positive refracting poweras a whole.

The image erecting means includes the prisms P1 and P2. In the realimage mode finder optical system of the eleventh embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P2 and the negative lens L1, and the field frame, suchas that shown in FIG. 4, is placed in the proximity of its imagingposition.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along theoptical path so that the optical axis is bent to obtain an erect image.For example, the prism P1 is provided with one reflecting surface (forbending the optical axis in the Y-Z plane) and the prism P2 is providedwith three reflecting surfaces (for bending the optical axis once in theY-Z plane and twice in the X-Z plane in this order from the object side)to erect the image. Also, the arrangement of the reflecting surfaces isbased on that of a Porro prism. Angles made with the optical axis bentby the reflecting surfaces are such that, for example, the angle of theoptical axis bent by the reflecting surface of the prism P1 is smallerthan 90 degrees, while the angles of the optical axis bent by tworeflecting surfaces of the prism P2 are larger than 90 degrees and theangle of the optical axis bent by the remaining one reflecting surfaceis smaller than 90 degrees. The reflecting surfaces making anglessmaller than 90 degrees are coated with metal films, such as silver andaluminum. The reflecting surfaces of angles larger than 90 degreesutilize total reflection. The cemented lens component CE is constructedso that diopter adjustment can be made in accordance with an observer'sdiopter.

In the eleventh embodiment, the cemented lens component CE including, inorder from the object side, the negative lens element and the positivelens element is used to suppress the chromatic aberration ofmagnification produced in the eyepiece optical system.

Also, aberration characteristics in the eleventh embodiment are shown inFIGS. 51A-51D, 52A-52D, 53A-53D, and 54-54D.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the eleventh embodimentare shown below.

Numerical data 11 Wide-angle position Middle position Telephoto positionm  0.685  1.175  2.016 ω (°) 26.509 15.216  8.803 f (mm) 10.289 17.62930.259 Pupil dia. (mm)  4.000 r₁ = −31.2936 d₁ = 1.3442 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 16.8814 (aspherical) d₂ = D2 (variable) r₃ = 14.1167(aspherical) d₃ = 4.5120 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −20.4840d₄ = D4 (variable) r₅ = −20.2406 d₅ = 0.9963 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 14.9676 (aspherical) d₆ = D6 (variable) r₇ = 41.4899 d₇ =14.6927 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −17.9428 (aspherical) d₈ =0.5000 r₉ = 34.5533 d₉ = 39.7402 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−28.4392 d₁₀ = 4.5510 r₁₁ = ∞ (field frame) d₁₁ = 7.9719 r₁₂ = −9.6322(aspherical) d₁₂ = 3.1829 n_(d12) = 1.58423 ν_(d12) = 30.49 r₁₃ =−10.6815 d₁₃ = 1.6105 r₁₄ = 19.4893 d₁₄ = 1.0000 n_(d14) = 1.58423ν_(d14) = 30.49 r₁₅ = 13.6490 d₁₅ = 5.4672 n_(d15) = 1.49241 ν_(d15) =57.66 r₁₆ = −12.4053 (aspherical) d₁₆ = 15.7651 r₁₇ = ∞ (eyepoint)Aspherical coefficients Second surface K = −1.3018 A₄ = −1.08269 × 10⁻⁴A₆ = 9.30175 × 10⁻⁷ A₈ = −1.42679 × 10⁻⁹ Third surface K = −0.1791 A₄ =−1.31719 × 10⁻⁴ A₆ = 1.67274 × 10⁻⁷ A₈ = −6.28754 × 10⁻¹⁰ Sixth surfaceK = −0.0761 A₄ = −1.10385 × 10⁻⁴ A₆ = −3.75495 × 10⁻⁷ A₈ = 2.90075 ×10⁻⁹ Eighth surface K = 0.1945 A₄ = 3.40022 × 10⁻⁵ A₆ = −8.32444 × 10⁻⁸A₈ = 2.90545 × 10⁻⁹ Twelfth surface K = 0.0000 A₄ = −2.80853 × 10⁻⁴ A₆ =−6.97108 × 10⁻⁶ Sixteenth surface K = 0.0000 A₄ = 3.07353 × 10⁻⁵ A₆ =9.18614 × 10⁻⁷ Wide-angle position Middle position Telephoto positionZoom data D2 25.8073 13.2103  8.2556 D4  0.9957  9.3832 20.5408 D6 3.5101  4.5817  1.6440 mh = 9.486 mm Conditions (1), (7) mh/fe = 0.632Conditions (2), (3) fe = 15.010 mm Conditions (5), (6) νp − νn = 27.17

Twelfth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 55A-55C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twelfth embodiment areshown below.

Numerical data 12 Wide-angle position Middle position Telephoto positionm  0.530  1.007  2.050 ω (°) 33.694 17.618  8.796 f (mm)  8.482 16.10032.782 Pupil dia. (mm)  4.000 r₁ = 52.6894 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 9.9227 (aspherical) d₂ = D2 (variable) r₃ = 10.2741(aspherical) d₃ = 4.2589 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −23.8681(aspherical) d₄ = D4 (variable) r₅ = −10.3480 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.6480 (aspherical) d₆ = D6(variable) r₇ = 11.1372 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−26.1339 (aspherical) d₈ = 0.5000 r₉ = 15.5869 (aspherical) d₉ = 22.3572n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.4528 r₁₁ = ∞ (fieldframe) d₁₁ = 3.0665 r₁₂ = 15.8132 (aspherical) d₁₂ = 15.9408 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −75.7570 d₁₃ = 2.0915 r₁₄ = 27.2996 d₁₄ =4.8098 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.0615 (aspherical) d₁₅= 16.8220 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2951 A₄ = 2.66909 × 10⁻⁵ A₆ = −2.25605 × 10⁻⁷ A₈ = 9.99104 × 10⁻¹¹Third surface K = −0.2614 A₄ = −8.86459 × 10⁻⁵ A₆ = −2.02523 × 10⁻⁷ A₈ =−5.25729 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 6.51575 × 10⁻⁵ A₆ =−1.53327 × 10⁻⁷ A₈ = −1.18392 × 10⁻⁹ Fifth surface K = 0.2138 A₄ =4.33241 × 10⁻⁴ A₆ = −1.93785 × 10⁻⁵ A₈ = 4.02985 × 10⁻⁷ Sixth surface K= −0.0427 A₄ = −9.91769 × 10⁻⁵ A₆ = −1.51811 × 10⁻⁵ A₈ = 3.40669 × 10⁻⁷Eighth surface K = 0.1565 A₄ = 2.28575 × 10⁻⁴ A₆ = −1.22359 × 10⁻⁷ A₈ =3.27751 × 10⁻⁸ Ninth surface K = 0.0140 A₄ = 4.56644 × 10⁻⁶ A₆ =−9.81069 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −7.24335 × 10⁻⁴ A₆ =3.64409 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.99493 × 10⁻⁵ A₆ =9.74998 × 10⁻⁸ Wide-angle Middle Telephoto position position positionZoom data D2   11.4582    6.8773    3.0038 D4    1.2808    8.5674  16.7674 D6    8.0121    5.3064    0.9799 mh = 10.692 mm f123 −11.144−21.243 −44.469 m23    0.529    1.000    2.038 m2  −1.000 m3  −1.000Condition (9) MG45 −0.763  −0.765  −0.767 Conditions (1), (7) mh/fe =0.669 Conditions (2), (3) fe = 15.991 mm Condition (8) φ (mh/2) =−0.406970 (1/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.389Condition (12) f2/f3 = −1.618 Condition (13) fw/fFw = −0.761 Condition(14) fT/fFT = −0.737 Condition (15) mT/mW = 3.865 Condition (16)fw/fw123 = −0.761 Condition (17) fT/fT123 = −0.737

Thirteenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 56A-56C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the thirteenth embodimentare shown below.

Numerical data 13 Wide-angle position Middle position Telephoto positionm  0.533  1.007  2.050 ω (°) 33.897 17.661  8.803 f (mm)  7.468 14.11128.722 Pupil dia. (mm)  4.000 r₁ = 166.7316 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.3218 (aspherical) d₂ = D2 (variable) r₃ = 10.2841(aspherical) d₃ = 4.3636 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −19.9166(aspherical) d₄ = D4 (variable) r₅ = −9.8214 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.1214 (aspherical) d₆ = D6(variable) r₇ = 13.2873 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−17.5762 (aspherical) d₈ = 0.5000 r₉ = 15.4406 (aspherical) d₉ = 22.6932n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1168 r₁₁ = ∞ (fieldframe) d₁₁ = 2.4325 r₁₂ = 28.5591 (aspherical) d₁₂ = 14.7924 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −24.5754 d₁₃ = 1.2620 r₁₄ = 27.5003 d₁₄ =4.1395 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.2956 (aspherical) d₁₅= 16.6524 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2951 A₄ = −9.85470 × 10⁻⁶ A₆ = −3.31289 × 10⁻⁷ A₈ = 3.00060 × 10⁻⁹Third surface K = −0.2607 A₄ = −9.27092 × 10⁻⁵ A₆ = −8.01222 × 10⁻⁷ A₈ =2.80942 × 10⁻⁹ Fourth surface K = −0.0224 A₄ = 1.02300 × 10⁻⁴ A₆ =−7.73167 × 10⁻⁷ A₈ = 5.82839 × 10⁻⁹ Fifth surface K = 0.2137 A₄ =5.86855 × 10⁻⁴ A₆ = −2.95943 × 10⁻⁵ A₈ = 6.45936 × 10⁻⁷ Sixth surface K= −0.0425 A₄ = −2.30372 × 10⁻⁵ A₆ = −2.55725 × 10⁻⁵ A₈ = 6.22366 × 10⁻⁷Eighth surface K = 0.1564 A₄ = 1.56106 × 10⁻⁴ A₆ = −7.63871 × 10⁻⁸ A₈ =4.09536 × 10⁻⁹ Ninth surface K = 0.0137 A₄ = 9.52536 × 10⁻⁷ A₆ =−1.05084 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −1.23450 × 10⁻³ A₆ =1.00000 × 10⁻⁵ Fifteenth surface K = 0.0000 A₄ = 3.90391 × 10⁻⁵ A₆ =1.54761 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.7540    7.4253    3.7541 D4    1.2500    8.1247  15.8923 D6    7.6424    5.0964    1.0000 mh = 9.279 mm f123 −10.011−18.982 −39.511 m23    0.531    1.000    2.036 m2  −1.000 m3  −1.000Condition (9) MG45 −0.748  −0.749  −0.751 Conditions (1), (7) mh/fe =0.662 Conditions (2), (3) fe = 14.010 mm Condition (8) φ (mh/2) =−0.395473 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.319Condition (12) f2/f3 = −1.622 Condition (13) fw/fFw = −0.746 Condition(14) fT/fFT = −0.727 Condition (15) mT/mW = 3.846 Condition (16)fw/fw123 = −0.746 Condition (17) fT/fT123 = −0.727

Fourteenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 57A-57C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the fourteenth embodimentare shown below.

Numerical data 14 Wide-angle position Middle position Telephoto positionm  0.530  1.011  2.054 ω (°) 33.791 17.591  8.810 f (mm)  7.962 15.17030.830 Pupil dia. (mm)  4.000 r₁ = 82.9717 d₁ = 1.0000 n_(d1) = 1.58425ν_(d1) = 30.35 r₂ = 10.0913 (aspherical) d₂ = D2 (variable) r₃ = 10.3969(aspherical) d₃ = 4.2911 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −21.6082(aspherical) d₄ = D4 (variable) r₅ = −11.4300 d₅ = 1.0000 n_(d5) =1.58425 ν_(d5) = 30.35 r₆ = 9.3984 (aspherical) d₆ = D6 (variable) r₇ =11.1076 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −24.3057(aspherical) d₈ = 0.5000 r₉ = 15.7603 (aspherical) d₉ = 22.4265 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.2691 r₁₁ = ∞ (field frame) d₁₁ =2.5500 r₁₂ = 15.9134 (aspherical) d₁₂ = 15.5881 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −39.1000 d₁₃ = 1.7582 r₁₄ = 25.7997 (aspherical)d₁₄ = 5.1865 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.7689(aspherical) d₁₅ = 16.8782 r₁₆ = ∞ (eyepoint) Aspherical coefficientsSecond surface K = −1.2943 A₄ = −9.84819 × 10⁻⁶ A₆ = −2.39182 × 10⁻⁸ A₈= 4.94427 × 10⁻¹⁰ Third surface K = −0.2438 A₄ = −1.13792 × 10⁻⁴ A₆ =−6.83279 × 10⁻⁸ A₈ = −6.63089 × 10⁻⁹ Fourth surface K = −0.0218 A₄ =6.76356 × 10⁻⁵ A₆ = −1.19790 × 10⁻⁷ A₈ = −2.64472 × 10⁻⁹ Sixth surface K= −0.0422 A₄ = −5.28848 × 10⁻⁴ A₆ = 2.13243 × 10⁻⁶ A₈ = 1.98353 × 10⁻⁸Eighth surface K = 0.1608 A₄ = 1.86541 × 10⁻⁴ A₆ = 1.81579 × 10⁻⁷ A₈ =3.74182 × 10⁻⁸ Ninth surface K = 0.0115 A₄ = −3.79724 × 10⁻⁵ A₆ =−6.23075 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fourteenth surface K = 0.0000 A₄ = 1.76029 × 10⁻⁵ A₆ =3.42514 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ = 6.14363 × 10⁻⁵ A₆ =4.37825 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   12.0419    7.5075    3.7196 D4    1.1332    8.3326  16.3538 D6    7.8982    5.2332    1.0000 mh = 10.098 mm f123 −10.392−19.874 −41.387 m23    0.526    1.000    2.034 m2  −1.000 m3  −1.000Condition (9) MG45 −0.768   −0.770   −0.772 Conditions (1), (7) mh/fe =0.673 Conditions (2), (3) fe = 15.010 mm Condition (8) φ (mh/2) =−0.377550 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.350Condition (12) f2/f3 = −1.615 Condition (13) fw/fFw = −0.766 Condition(14) fT/fFT = −0.745 Condition (15) mT/mW = 3.872 Condition (16)fw/fw123 = −0.766 Condition (17) fT/fT123 = −0.745

Fifteenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 58A-58C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the fifteenth embodimentare shown below.

Numerical data 15 Wide-angle position Middle position Telephoto positionm  0.429  0.813  1.663 ω (°) 33.665 17.724  8.889 f (mm)  7.384 13.99728.641 Pupil dia. (mm)  4.000 r₁ = 107.4567 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.2589 (aspherical) d₂ = D2 (variable) r₃ = 10.2029(aspherical) d₃ = 4.4631 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −20.4728(aspherical) d₄ = D4 (variable) r₅ = −9.3096 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3604 (aspherical) d₆ = D6(variable) r₇ = 16.9815 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−13.8071 (aspherical) d₈ = 0.5000 r₉ = 15.6162 (aspherical) d₉ = 22.4902n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3198 r₁₁ = ∞ (fieldframe) d₁₁ = 3.8080 r₁₂ = 24.6624 (aspherical) d₁₂ = 15.9445 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −144.7239 d₁₃ = 2.0644 r₁₄ = 37.1434 d₁₄ =4.1276 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.1033 (aspherical) d₁₅= 16.7947 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2993 A₄ = 5.71536 × 10⁻⁵ A₆ = −1.74731 × 10⁻⁶ A₈ = 9.48321 × 10⁻⁹Third surface K = −0.2562 A₄ = −1.82646 × 10⁻⁵ A₆ = −1.79005 × 10⁻⁶ A₈ =5.13165 × 10⁻⁹ Fourth surface K = −0.0200 A₄ = 1.47200 × 10⁻⁴ A₆ =−1.56976 × 10⁻⁶ A₈ = 1.27897 × 10⁻⁸ Fifth surface K = 0.2127 A₄ =5.41270 × 10⁻⁴ A₆ = −3.32639 × 10⁻⁵ A₈ = 5.81147 × 10⁻⁷ Sixth surface K= −0.0433 A₄ = −1.09499 × 10⁻⁴ A₆ = −2.68424 × 10⁻⁵ A₈ = 6.74415 × 10⁻⁷Eighth surface K = 0.1546 A₄ = 2.00697 × 10⁻⁴ A₆ = −1.61566 × 10⁻⁶ A₈ =−3.13569 × 10⁻⁹ Ninth surface K = 0.0164 A₄ = 6.95918 × 10⁻⁵ A₆ =−2.13186 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −4.54314 × 10⁻⁴ A₆ =−3.43968 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.97954 × 10⁻⁵ A₆ =1.10003 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.2714    6.9682    3.2721 D4    1.6105    8.4616  16.2351 D6    7.6649    5.1170    1.0397 mh = 9.349 mm f123 −10.318−19.605 −41.020 m23    0.530    1.000    2.042 m2  −1.000 m3  −1.000Condition (9) MG45 −0.717  −0.720  −0.722 Conditions (1), (7) mh/fe =0.543 Conditions (2), (3) fe = 17.226 mm Condition (8) φ (mh/2) =−0.390191 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.335Condition (12) f2/f3 = −1.656 Condition (13) fw/fFw = −0.716 Condition(14) fT/fFT = −0.698 Condition (15) mT/mW = 3.879 Condition (16)fw/fw123 = −0.716 Condition (17) fT/fT123 = −0.698

Sixteenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 59A-59C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the sixteenth embodimentare shown below.

Numerical data 16 Wide-angle position Middle position Telephoto positionm  0.429  0.809  2.024 ω (°) 33.860 17.674  7.199 f (mm)  7.439 14.04735.124 Pupil dia. (mm)  4.000 r₁ = 244.6491 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.7182 (aspherical) d₂ = D2 (variable) r₃ = 9.8239(aspherical) d₃ = 4.5281 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −19.6580(aspherical) d₄ = D4 (variable) r₅ = −9.4259 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.7259 (aspherical) d₆ = D6(variable) r₇ = 13.6837 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−17.5090 (aspherical) d₈ = 0.5000 r₉ = 15.6690 (aspherical) d₉ = 22.4657n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3443 r₁₁ = ∞ (fieldframe) d₁₁ = 4.2463 r₁₂ = 24.2774 (aspherical) d₁₂ = 15.9476 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −225.2944 d₁₃ = 2.0463 r₁₄ = 37.1333 d₁₄ =3.6458 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.1787 (aspherical) d₁₅= 16.8295 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.3022 A₄ = 1.94109 × 10⁻⁵ A₆ = −1.53742 × 10⁻⁶ A₈ = 9.18621 × 10⁻⁹Third surface K = −0.2549 A₄ = −7.62311 × 10⁻⁵ A₆ = −2.11044 × 10⁻⁶ A₈ =9.22506 × 10⁻⁹ Fourth surface K = −0.0175 A₄ = 1.18065 × 10⁻⁴ A₆ =−1.28525 × 10⁻⁶ A₈ = 1.15858 × 10⁻⁸ Fifth surface K = 0.2594 A₄ =7.73262 × 10⁻⁴ A₆ = −4.07569 × 10⁻⁵ A₈ = 6.35774 × 10⁻⁷ Sixth surface K= −0.0434 A₄ = 2.49683 × 10⁻⁵ A₆ = −3.63701 × 10⁻⁵ A₈ = 8.31505 × 10⁻⁷Eighth surface K = 0.1534 A₄ = 1.67581 × 10⁻⁴ A₆ = −1.34210 × 10⁻⁶ A₈ =5.76435 × 10⁻⁹ Ninth surface K = 0.0177 A₄ = 9.17386 × 10⁻⁶ A₆ =−1.80151 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −3.02442 × 10⁻⁴ A₆ =−2.91068 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 5.38216 × 10⁻⁵ A₆ =6.59977 × 10⁻⁸ Wide-angle Middle Telephoto position position positionZoom data D2   10.3532    6.2169    1.8288 D4    1.2500    7.8558  17.6530 D6    8.8787    6.4091    1.0000 mh = 9.259 mm f123 −10.214−19.332 −50.207 m23    0.532    1.000    2.500 m2  −1.000 m3  −1.000Condition (9) MG45 −0.730  −0.732  −0.735 Conditions (1), (7) mh/fe =0.534 Conditions (2), (3) fe = 17.354 mm Condition (8) φ (mh/2) =−0.263294 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.334Condition (12) f2/f3 = −1.638 Condition (13) fw/fFw = −0.728 Condition(14) fT/fFT = −0.700 Condition (15) mT/mW = 4.722 Condition (16)fw/fw123 = −0.728 Condition (17) fT/fT123 = −0.700

Seventeenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 60A-60C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the seventeenth embodimentare shown below.

Numerical data 17 Wide-angle position Middle position Telephoto positionm  0.427  0.806  2.149 ω (°) 34.100 17.683  6.723 f (mm)  7.358 13.90137.053 Pupil dia. (mm)  4.000 r₁ = −713.7698 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 11.0797 (aspherical) d₂ = D2 (variable) r₃ =9.7135 (aspherical) d₃ = 4.6200 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−18.4096 (aspherical) d₄ = D4 (variable) r₅ = −9.1335 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.4327 (aspherical) d₆ = D6(variable) r₇ = 13.0353 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−18.2574 (aspherical) d₈ = 0.5000 r₉ = 15.8017 (aspherical) d₉ = 22.4291n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3809 r₁₁ = ∞ (fieldframe) d₁₁ = 4.1914 r₁₂ = 23.7178 (aspherical) d₁₂ = 15.9419 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −188.7242 d₁₃ = 2.0225 r₁₄ = 38.0414 d₁₄ =3.6351 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.0922 (aspherical) d₁₅= 16.8589 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.3025 A₄ = −3.21798 × 10⁻⁵ A₆ = −7.78889 × 10⁻⁷ A₈ = 5.08606 × 10⁻⁹Third surface K = −0.2547 A₄ = −1.33313 × 10⁻⁴ A₆ = −1.48099 × 10⁻⁶ A₈ =7.55992 × 10⁻⁹ Fourth surface K = −0.0172 A₄ = 1.11743 × 10⁻⁴ A₆ =−9.24392 × 10⁻⁷ A₈ = 9.33552 × 10⁻⁹ Fifth surface K = 0.2714 A₄ =1.27697 × 10⁻³ A₆ = −8.18736 × 10⁻⁵ A₈ = 1.94631 × 10⁻⁶ Sixth surface K= −0.0432 A₄ = 3.65213 × 10⁻⁴ A₆ = −6.62961 × 10⁻⁵ A₈ = 1.63076 × 10⁻⁶Eighth surface K = 0.1534 A₄ = 1.31305 × 10⁻⁴ A₆ = −7.77237 × 10⁻⁷ A₈ =1.72405 × 10⁻⁸ Ninth surface K = 0.0176 A₄ = −4.34110 × 10⁻⁵ A₆ =−9.40302 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −2.47396 × 10⁻⁴ A₆ =−3.97394 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 5.72418 × 10⁻⁵ A₆ =3.57168 × 10⁻⁸ Wide-angle Middle Telephoto position position positionZoom data D2   10.0156    5.9870    1.4776 D4    1.2500    7.6739  17.9124 D6    9.1244    6.7292    1.0000 mh = 9.156 mm f123  −9.916−18.774 −52.236 m23    0.532    1.000    2.667 m2  −1.000 m3  −1.000Condition (9) MG45 −0.744  −0.746  −0.748 Conditions (1), (7) mh/fe =0.531 Conditions (2), (3) fe = 17.239 mm Condition (8) φ (mh/2) =−0.251090 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.309Condition (12) f2/f3 = −1.647 Condition (13) fw/fFw = −0.742 Condition(14) fT/fFT = −0.709 Condition (15) mT/mW = 5.035 Condition (16)fw/fw123 = −0.742 Condition (17) fT/fT123 = −0.709

Eighteenth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 61A-61C, has nearly the same arrangement as that of the firstembodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the eighteenth embodimentare shown below.

Numerical data 18 Wide-angle position Middle position Telephoto positionm  0.435  0.824  1.691 ω (°) 33.426 17.596  8.847 f (mm)  7.656 14.49829.743 Pupil dia. (mm)  4.000 r₁ = 99.5495 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.1706 (aspherical) d₂ = D2 (variable) r₃ = 10.3729(aspherical) d₃ = 4.4126 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −19.6559(aspherical) d₄ = D4 (aspherical) r₅ = −9.5997 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 9.8997 (aspherical) d₆ = D6(variable) r₇ = 14.3933 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−15.6309 (aspherical) d₈ = 0.5000 r₉ = 15.7116 (aspherical) d₉ = 22.4940n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.3160 r₁₁ = ∞ (fieldframe) d₁₁ = 3.6826 r₁₂ = 27.7932 (aspherical) d₁₂ = 16.0681 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −173.7673 d₁₃ = 2.3552 r₁₄ = 35.5235 d₁₄ =4.0389 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −14.3073 (aspherical) d₁₅= 22.5403 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.3005 A₄ = 6.14835 × 10⁻⁵ A₆ = −1.68311 × 10⁻⁶ A₈ = 8.77195 × 10⁻⁹Third surface K = −0.2546 A₄ = −2.04009 × 10⁻⁶ A₆ = −1.97626 × 10⁻⁶ A₈ =8.97003 × 10⁻⁹ Fourth surface K = −0.0188 A₄ = 1.56534 × 10⁻⁴ A₆ =−1.56324 × 10⁻⁶ A₈ = 1.26722 × 10⁻⁸ Fifth surface K = 0.2126 A₄ =4.66912 × 10⁻⁴ A₆ = −3.86240 × 10⁻⁵ A₈ = 1.14314 × 10⁻⁶ Sixth surface K= −0.0436 A₄ = −2.20422 × 10⁻⁴ A₆ = −2.72889 × 10⁻⁵ A₈ = 8.43830 × 10⁻⁷Eighth surface K = 0.1534 A₄ = 2.24324 × 10⁻⁴ A₆ = −3.90532 × 10⁻⁶ A₈ =2.12435 × 10⁻⁸ Ninth surface K = 0.0178 A₄ = 4.50620 × 10⁻⁵ A₆ =−3.09867 × 10⁻⁶ Twelfth surface K = 0.0000 A₄ = −7.56343 × 10⁻⁴ A₆ =8.42941 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ = 3.82666 × 10⁻⁵ A₆ =2.37037 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.1798    6.8982    3.2011 D4    1.7379    8.5495  16.3243 D6    7.6797    5.1496    1.0719 mh = 9.800 mm f123 −10.319−19.589 −41.128 m23    0.530    1.000    2.048 m2  −1.000 m3  −1.000Condition (9) MG45 −0.744  −0.746  −0.749 Conditions (1), (7) mh/fe =0.557 Conditions (2), (3) fe = 17.593 mm Condition (8) φ (mh/2) =−0.484313 (l/mm) Condition (10) β3 = −1.000 Condition (11) SF2 = −0.309Condition (12) f2/f3 = −1.663 Condition (13) fw/fFw = −0.742 Condition(14) fT/fFT = −0.723 Condition (15) mT/mW = 3.885 Condition (16)fw/fw123 = −0.742 Condition (17) fT/fT123 = −0.723

Nineteenth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 62A-62C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the nineteenthembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the prism P, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the fourth unitG4 and by moving the first unit G1, the second unit G2, and the thirdunit G3 along the optical axis. In this case, the second unit G2 issimply moved toward the object side, and the third unit G3 toward theeyepiece side.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havecurvatures. The entrance surface and the exit surface of the prism Palso have curvatures.

The prisms P1 and P2 and the prism P are provided with the samereflecting surfaces as the reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁in the first embodiment shown in FIGS. 1-3, along the optical path, sothat the optical axis is bent to erect an image. For example, onereflecting surface provided in the prism P1 bends the optical axis inthe Y-Z plane; two reflecting surfaces provided in the prism P2 bend theoptical axis in the Y-Z plane and the X-Z plane in this order from theobject side; and one reflecting surface provided in the prism P bendsthe optical axis in the X-Z plane. In this way, an erect image isobtained. Also, the arrangement of the reflecting surfaces is based onthat of a Porro prism. Angles made with the optical axis bent by thereflecting surfaces are such that, for example, the angles of theoptical axis bent by the reflecting surfaces of the prism P1 and theprism P are smaller than 90 degrees and the angles of the optical axisbent by the reflecting surfaces of the prism P2 are larger than 90degrees. The reflecting surfaces of the prism P1 and the prism P arecoated with metal films, such as silver and aluminum. The two reflectingsurfaces of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface of the prismP2 may be made smaller than 90 degrees so that this reflecting surfaceis coated with a metal film. Moreover, the angle of the optical axisbent by the reflecting surface of the prism P may also be made largerthan 90 degrees so that this reflecting surface utilizes totalreflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the nineteenth embodimentare shown below.

Numerical data 19 Wide-angle position Middle position Telephoto positionm  0.528  1.033  2.073 ω (°) 33.663 17.287  8.778 f (mm)  7.927 15.50331.114 Pupil dia. (mm)  4.000 r₁ = 38.8071 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 8.9754 (aspherical) d₂ = D2 (variable) r₃ = 9.9087(aspherical) d₃ = 4.3628 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −23.7155(aspherical) d₄ = D4 (variable) r₅ = −10.0428 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3428 (aspherical) d₆ = D6(variable) r₇ = 11.5157 d₇ = 9.9000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−22.7435 (aspherical) d₈ = 0.5000 r₉ = 15.4370 (aspherical) d₉ = 22.2718n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1155 r₁₁ = ∞ (fieldframe) d₁₁ = 2.3895 r₁₂ = 18.2155 (aspherical) d₁₂ = 15.5672 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −36.4337 d₁₃ = 1.8054 r₁₄ = 26.1660 d₁₄ =4.9762 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.4971 (aspherical) d₁₅= 16.9055 r₁₆ = ∞ (eyepoint) Aspherical coefficients Second surface K =−1.2947 A₄ = 2.38204 × 10⁻⁵ A₆ = 4.87600 × 10⁻⁷ A₈ = −3.73584 × 10⁻⁹Third surface K = −0.2620 A₄ = −1.35699 × 10⁻⁴ A₆ = 4.65011 × 10⁻⁷ A₈ =−1.87327 × 10⁻⁸ Fourth surface K = −0.0225 A₄ = 4.04582 × 10⁻⁵ A₆ =7.12976 × 10⁻⁸ A₈ = −9.76450 × 10⁻⁹ Fifth surface K = 0.2139 A₄ =6.19005 × 10⁻⁴ A₆ = −3.14679 × 10⁻⁵ A₈ = 7.58697 × 10⁻⁷ Sixth surface K= −0.0424 A₄ = 4.58626 × 10⁻⁵ A₆ = −2.40512 × 10⁻⁵ A₈ = 5.34729 × 10⁻⁷Eighth surface K = 0.1566 A₄ = 2.05649 × 10⁻⁴ A₆ = 2.93949 × 10⁻⁷ A₈ =2.68796 × 10⁻⁸ Ninth surface K = 0.0143 A₄ = 7.12313 × 10⁻⁶ A₆ =−6.74794 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −1.15138 × 10⁻³ A₆ =8.42829 × 10⁻⁶ Fifteenth surface K = 0.0000 A₄ = 4.56110 × 10⁻⁵ A₆ =1.18793 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.7539    7.0573    3.4654 D4    1.2500    8.5614  16.1337 D6    8.1857    5.3729    1.0000 mh = 10.076 mm f123 −10.700−21.016 −43.277 m23    0.529    1.032    2.072 m2  −1.000 m3  −1.032Condition (9) MG45 −0.743  −0.744  −0.746 Conditions (1), (7) mh/fe =0.671 Conditions (2), (3) fe = 15.009 mm Condition (8) φ (mh/2) =−0.451821 (l/mm) Condition (10) β3 = −1.032 Condition (11) SF2 = −0.411Condition (12) f2/f3 = −1.625 Condition (13) fw/fFw = −0.741 Condition(14) fT/fFT = −0.719 Condition (15) mT/mW = 3.925 Condition (16)fw/fw123 = −0.741 Condition (17) fT/fT123 = −0.719

Twentieth Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 63A-63C, has nearly the same arrangement as that of thenineteenth embodiment with the exception of lens data. A substantialdifference with the nineteenth embodiment is that the exit surface ofthe prism P2 has a curvature in twentieth embodiment.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twentieth embodimentare shown below.

Numerical data 20 Wide-angle position Middle position Telephoto positionm  0.557  1.038  2.023 ω (°) 32.360 17.517  9.010 f (mm)  8.356 15.58430.363 Pupil dia. (mm)  4.000 r₁ = 59.2465 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 8.3310 (aspherical) d₂ = D2 (variable) r₃ = 8.3856(aspherical) d₃ = 4.1672 n_(d3) = 1.49241 ν_(d3) = 57.66 r₄ = −17.8798d₄ = D4 (variable) r₅ = −13.7008 d₅ = 0.7000 n_(d5) = 1.58423 ν_(d5) =30.49 r₆ = 8.6409 (aspherical) d₆ = D6 (variable) r₇ = 11.7739 d₇ =9.8661 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −29.5195 (aspherical) d₈ =1.0000 r₉ = 15.0708 d₉ = 22.3752 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ =−416.8001 d₁₀ = 2.0410 r₁₁ = ∞ (field frame) d₁₁ = 2.4340 r₁₂ = 15.7244(aspherical) d₁₂ = 18.3578 n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ =−20.5538 d₁₃ = 1.2739 r₁₄ = 30.8079 (aspherical) d₁₄ = 3.4263 n_(d14) =1.52542 ν_(d14) = 55.78 r₁₅ = −24.2754 (aspherical) d₁₅ = 15.7651 r₁₆ =∞ (eyepoint) Aspherical coefficients Second surface K = −1.3070 A₄ =−5.42129 × 10⁻⁵ A₆ = 2.66433 × 10⁻⁶ A₈ = −1.96586 × 10⁻⁸ Third surface K= −0.2445 A₄ = −3.33944 × 10⁻⁴ A₆ = 3.11379 × 10⁻⁷ A₈ = −1.64750 × 10⁻⁸Sixth surface K = −0.0650 A₄ = −5.31385 × 10⁻⁴ A₆ = 4.99350 × 10⁻⁶ A₈ =−6.09994 × 10⁻⁸ Eighth surface K = 0.1673 A₄ = 2.10857 × 10⁻⁴ A₆ =1.83918 × 10⁻⁷ A₈ = 3.12747 × 10⁻⁸ Twelfth surface K = 0.0000 A₄ =−1.45924 × 10⁻³ A₆ = 1.59291 × 10⁻⁵ Fourteenth K = 0.0000 A₄ = 7.03020 ×10⁻⁵ A₆ = 4.89240 × 10⁻⁷ Fifteenth K = 0.0000 A₄ = 8.28668 × 10⁻⁵ A₆ =3.99233 × 10⁻⁷ Wide-angle Middle Telephoto position position positionZoom data D2   11.8115    7.0078    2.9081 D4    1.0094    6.6799  14.3532 D6    7.7860    4.6744    1.0000 mh = 9.992 mm f123 −12.274−23.044 −46.120 m23    0.734    1.370    2.676 m2  −1.000 m3  −1.370Condition (9) MG45 −0.683  −0.683  −0.683 Conditions (1), (7) mh/fe =0.666 Conditions (2), (3) fe = 15.010 mm Condition (8) φ (mh/2) =−0.322195 (l/mm) Condition (10) β3 = −1.370 Condition (11) SF2 = −0.361Condition (12) f2/f3 = −1.364 Condition (13) fw/fFw = −0.681 Condition(14) fT/fFT = −0.658 Condition (15) mT/mW = 3.634 Condition (16)fw/fw123 = −0.681 Condition (17) fT/fT123 = −0.658

Twenty-First Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 64A-64C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with two prisms P1 and P2. Theeyepiece optical system is constructed with the prism P and the positivelens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P.In the real image mode finder optical system of the twenty-firstembodiment, the intermediate image formed by the objective opticalsystem is interposed between the prism P2 and the positive lens E1, andthe field frame, such as that shown in FIG. 4, is provided in theproximity of its imaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface and the exitsurface of the prism P1 and the entrance surface of the prism P2 havecurvatures. The entrance surface and the exit surface of the prism Palso have curvatures.

The prisms P1 and P2 and the prism P, as shown in FIGS. 65-67, areprovided with reflecting surfaces P1 ₁, P2 ₁, P2 ₂, and P₁ along theoptical path so that the optical axis is bent to erect an image.Specifically, as shown in FIG. 66, the reflecting surface P1 ₁ providedin the prism P1 bends the optical axis in a Y-Z plane; as shown in FIG.67, the two reflecting surfaces P2 ₁ and P2 ₂ provided in the prism P2bend the optical axis twice in the X-Y plane in this order from theobject side; and as shown in FIG. 66, the reflecting surface P₁ providedin the prism P bends the optical axis in the Y-Z plane. In this way, anerect image is obtained. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are 90 degrees. The reflectingsurfaces P1 ₁, P2 ₁, and P2 ₂ of the prism P1 and the prism P2 arecoated with metal films, such as silver and aluminum. The reflectingsurface P₁ of the prism P utilizes total reflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by one reflecting surface of the prism P2 may be made smallerthan 90 degrees so that this reflecting surface is coated with a metalfilm. Moreover, the angle of the optical axis bent by the otherreflecting surface of the prism P2 may also be made larger than 90degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twenty-firstembodiment are shown below.

Numerical data 21 Wide-angle position Middle position Telephoto positionm  0.394  0.659  1.049 ω (°) 32.118 19.007 12.091 f (mm)  6.866 11.49218.288 Pupil dia. (mm)  5.000 r₁ = −59.3919 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 10.3748 8 (aspherical) d₂ = D2 (variable) r₃ =14.1522 (aspherical) d₃ = 3.7000 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−9.2660 (aspherical) d₄ = D4 (variable) r₅ = −7.5095 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 13.7636 d₆ = D6 (variable)r₇ = 20.3870 d₇ = 10.0000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −13.4385(aspherical) d₈ = 0.4000 r₉ = 12.4702 (aspherical) d₉ = 22.0000 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.0000 r₁₁ = ∞ (field frame) d₁₁ =7.9991 r₁₂ = −18.8914 (aspherical) d₁₂ = 3.1688 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −15.1681 d₁₃ = 2.0000 r₁₄ = −13.4956 (aspherical)d₁₄ = 12.2000 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −10.7971(aspherical) d₁₅ = 13.5000 r₁₆ = ∞ (eyepoint) Aspherical coefficientsSecond surface K = −1.8801 A₄ = 8.93195 × 10⁻⁵ A₆ = −1.59803 × 10⁻⁵ A₈ =2.26734 × 10⁻⁷ Third surface K = −26.0761 A₄ = 8.01991 × 10⁻⁴ A₆ =−1.09865 × 10⁻⁴ A₈ = 4.19307 × 10⁻⁶ A₁₀ = −1.65929 × 10⁻⁷ Fourth surfaceK = 0.7079 A₄ = 1.90150 × 10⁻⁴ A₆ = −3.87917 × 10⁻⁵ A₈ = 8.76025 × 10⁻⁷A₁₀ = −3.24756 × 10⁻⁸ Fifth surface K = −0.4742 A₄ = 4.50016 × 10⁻⁴ A₆ =4.48738 × 10⁻⁵ A₈ = −3.79556 × 10⁻⁶ Eighth surface K = 0.8140 A₄ =−1.12430 × 10⁻³ A₆ = 5.37408 × 10⁻⁵ A₈ = −1.01121 × 10⁻⁶ Ninth surface K= −2.4434 A₄ = −1.05938 × 10⁻³ A₆ = 4.60167 × 10⁻⁵ A₈ = −8.38383 × 10⁻⁷Twelfth surface K = 0.0000 A₄ = 4.97477 × 10⁻⁴ A₆ = −3.14535 × 10⁻⁵ A₈ =−3.04078 × 10⁻⁸ Fourteenth surface K = 0.0000 A₄ = −8.27827 × 10⁻⁴ A₆ =5.41341 × 10⁻⁵ A₈ = −6.06561 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ = −4.89807 × 10⁻⁶ A₆ = 7.07749 × 10⁻⁶ A₈ = −9.70475 × 10⁻⁸ Wide-angleMiddle Telephoto position position position Zoom data D2   8.2666   5.9354    3.4477 D4   0.8000    5.6220   10.2589 D6   5.3399   2.8492    0.7000 mh = 8.240 mm f123 −9.787 −16.419 −26.311 m23  0.651    1.088    1.729 m2  −1.000 m3  −1.088 Condition (9) MG45−0.703  −0.704  −0.705 Conditions (1), (7) mh/fe = 0.473 Conditions (2),(3) fe = 17.434 mm Condition (10) β3 = −1.088 Condition (11) SF2 = 0.209Condition (12) f2/f3 = −1.379 Condition (13) fw/fFw = −0.702 Condition(14) fT/fFT = −0.695 Condition (15) mT/mW = 2.663 Condition (16)fw/fw123 = −0.702 Condition (17) fT/fT123 = −0.695

Twenty-Second Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 68A-68C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with the positive lens L1 and theprism P1. The eyepiece optical system is constructed with the prism Pand the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prism P1 and the prism P. In thereal image mode finder optical system of the second embodiment, theintermediate image formed by the objective optical system is interposedbetween the prism P1 and the prism P, and the field frame, such as thatshown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface of the prism P1 hasa curvature. The entrance surface and the exit surface of the prism Palso have curvatures.

The prism P1 and the prism P are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with three reflectingsurfaces for bending the optical axis twice in the Y-Z plane and once inthe X-Z plane in this order from the object side, and the prism P isprovided with one reflecting surface for bending the optical axis in theX-Z plane to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangle of the optical axis bent by one reflecting surface of the prism P1is smaller than 90 degrees and the angles of the optical axis bent bythe remaining two reflecting surfaces are larger than 90 degrees, whilethe angle of the optical axis bent by the reflecting surface of theprism P is smaller than 90 degrees. The reflecting surfaces makingangles smaller than 90 degrees are coated with metal films, such assilver and aluminum. The reflecting surfaces of angles larger than 90degrees utilize total reflection.

However, the angles of the optical axis bent by the reflecting surfacesare not limited to the above description. For example, the angle of theoptical axis bent by the most field-frame-side reflecting surface of theprism P1 may be made smaller than 90 degrees so that this reflectingsurface is coated with a metal film. Moreover, the angle of the opticalaxis bent by the reflecting surface of the prism P may also be madelarger than 90 degrees so that this reflecting surface utilizes totalreflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twenty-secondembodiment are shown below.

Numerical data 22 Wide-angle position Middle position Telephoto positionm  0.710  1.045  2.031 ω (°) 26.166 17.592  9.011 f (mm) 10.647 15.66330.438 Pupil dia. (mm)  4.000 r₁ = 94.9717 d₁ = 0.9721 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 9.3965 (aspherical) d₂ = D2 (variable) r₃ = 9.8091(aspherical) d₃ = 4.2874 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −25.4274(aspherical) d₄ = D4 (variable) r₅ = −16.9121 d₅ = 1.0000 n_(d5) =1.58423 ν_(d5) = 30.49 r₆ = 15.2040 (aspherical) d₆ = D6 (variable) r₇ =40.9744 d₇ = 3.5824 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ = −14.7461(aspherical) d₈ = 0.5000 r₉ = 21.4998 (aspherical) d₉ = 28.4133 n_(d9) =1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 1.8195 r₁₁ = ∞ (field frame) d₁₁ =2.3065 r₁₂ = 15.5002 (aspherical) d₁₂ = 15.7893 n_(d12) = 1.52542ν_(d12) = 55.78 r₁₃ = −35.0088 d₁₃ = 1.9666 r₁₄ = 27.5692 (aspherical)d₁₄ = 5.0860 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ = −16.2713(aspherical) d₁₅ = 16.9035 r₁₆ = ∞ (eyepoint) Aspherical coefficientsSecond surface K = −1.2960 A₄ = 2.42034 × 10⁻⁵ A₆ = −4.03294 × 10⁻⁷ A₈ =−3.85761 × 10⁻¹⁰ Third surface K = −0.2523 A₄ = −1.40079 × 10⁻⁴ A₆ =9.09631 × 10⁻⁸ A₈ = −7.25698 × 10⁻⁹ Fourth surface K = −0.0226 A₄ =2.34829 × 10⁻⁵ A₆ = 6.60458 × 10⁻⁷ A₈ = −6.09388 × 10⁻⁹ Sixth surface K= −0.0504 A₄ = −1.07083 × 10⁻⁴ A₆ = 1.32744 × 10⁻⁶ A₈ = −4.22406 × 10⁻⁹Eighth surface K = 0.1637 A₄ = 5.89020 × 10⁻⁵ A₆ = 2.51165 × 10⁻⁷ A₈ =1.03528 × 10⁻⁸ Ninth surface K = 0.0039 A₄ = −3.04882 × 10⁻⁶ A₆ =4.78283 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ = −1.19998 × 10⁻³ A₆ =1.07234 × 10⁻⁵ Fourteenth surface K = 0.0000 A₄ = 3.35581 × 10⁻⁵ A₆ =−1.60128 × 10⁻⁷ Fifteenth surface K = 0.0000 A₄ = 7.31972 × 10⁻⁵ A₆ =9.93972 × 10⁻⁹ Wide-angle Middle Telephoto position position positionZoom data D2  8.3076  6.0828  3.0961 D4  1.1490  6.5799  16.8299 D6 11.9688  8.7628  1.4995 mh = 9.844 mm f123 −21.628 −32.011 −64.323 m23 1.204  1.771  3.458 m2  −1.328 m3  −1.333 Condition (9) MG45 −0.495 −0.495  −0.495 Conditions (1), (7) mh/fe = 0.657 Conditions (2), (3) fe= 14.990 mm Condition (11) SF2 = −0.443 Condition (12) F2/f3 = −1.038Condition (13) fw/fFw = −0.492 Condition (14) fT/fFT = −0.473 Condition(15) mT/mW = 2.859 Condition (16) fw/fw123 = −0.492 Condition (17)fT/fT123 = −0.473

Twenty-Third Embodiment

The real image mode finder optical system of this embodiment, as shownin FIGS. 69A-69C, has nearly the same arrangement as that of thetwenty-first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twenty-thirdembodiment are shown below.

Numerical data 23 Wide-angle position Middle position Telephoto positionm  0.574  0.905  1.568 ω (°) 24.652 15.498  8.841 f (mm) 10.617 16.72528.996 Pupil dia. (mm)  4.000 r₁ = −920.9537 d₁ = 1.0000 n_(d1) =1.58423 ν_(d1) = 30.49 r₂ = 9.9330 (aspherical) d₂ = D2 (variable) r₃ =9.6882 (aspherical) d₃ = 4.1510 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ =−23.0106 (aspherical) d₄ = D4 (variable) r₅ = −14.4812 (aspherical) d₅ =1.0000 n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 14.7812 (aspherical) d₆ = D6(variable) r₇ = 11.6881 d₇ = 10.4000 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈= −44.1162 (aspherical) d₈ = 0.5000 r₉ = 19.0394 (aspherical) d₉ =21.0918 n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.9577 r₁₁ = ∞(field frame) d₁₁ = 8.6051 r₁₂ = 18.8914 (aspherical) d₁₂ = 3.0466n_(d12) = 1.52542 ν_(d12) = 55.78 r₁₃ = −19.3762 d₁₃ = 2.5000 r₁₄ =−22.1615 (aspherical) d₁₄ = 14.0000 n_(d14) = 1.52542 ν_(d14) = 55.78r₁₅ = −13.1330 (aspherical) d₁₅ = 16.9541 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2958 A₄ = −1.37883 × 10⁻⁴ A₆ =3.49813 × 10⁻⁶ A₈ = −2.85996 × 10⁻⁸ Third surface K = −0.2610 A₄ =−2.84178 × 10⁻⁴ A₆ = 2.18425 × 10⁻⁶ A₈ = 1.89724 × 10⁻⁸ Fourth surface K= −0.0222 A₄ = −3.94404 × 10⁻⁵ A₆ = 2.36146 × 10⁻⁶ A₈ = 1.07129 × 10⁻⁸Fifth surface K = 0.2136 A₄ = 7.49839 × 10⁻⁴ A₆ = −3.41182 × 10⁻⁵ A₈ =9.01815 × 10⁻⁷ Sixth surface K = −0.0419 A₄ = 6.33920 × 10⁻⁴ A₆ =−3.96052 × 10⁻⁵ A₈ = 1.13002 × 10⁻⁶ Eighth surface K = 0.1567 A₄ =1.02994 × 10⁻⁴ A₆ = 3.46598 × 10⁻⁶ A₈ = 6.31270 × 10⁻⁹ Ninth surface K =0.0129 A₄ = −6.13561 × 10⁻⁵ A₆ = 1.96098 × 10⁻⁶ Twelfth surface K =0.0000 A₄ = −1.14754 × 10⁻⁴ A₆ = 2.96268 × 10⁻⁶ A₈ = −4.33585 × 10⁻⁸Fourteenth surface K = 0.0000 A₄ = −1.44350 × 10⁻⁴ A₆ = −3.21946 × 10⁻⁶A₈ = 6.14512 × 10⁻⁸ Fifteenth surface K = 0.0000 A₄ = −7.32422 × 10⁻⁶ A₆= 5.88495 × 10⁻⁷ A₈ = −9.09150 × 10⁻¹⁰ Wide-angle Middle Telephotoposition position position Zoom data D2  8.4479  5.9380  3.5969 D4 2.3409  8.3613  16.2888 D6  10.0702  6.5597  0.9733 mh = 9.332 mm f123−20.012 −31.646 −56.048 m23  1.168  1.864  3.229 m2  −1.365 m3  −1.365Condition (9) MG45 −0.533  −0.535  −0.537 Conditions (1), (7) mh/fe =0.505 Conditions (2), (3) fe = 18.490 mm Condition (11) SF2 = −0.407Condition (12) F2/f3 = −1.097 Condition (13) fw/fFw = −0.530 Condition(14) fT/fFT = −0.517 Condition (15) mT/mW = 2.731 Condition (16)fw/fw123 = −0.530 Condition (17) fT/fT123 = −0.517

Twenty-Fourth Embodiment

In the real image mode finder optical system of this embodiment, asshown in FIGS. 70A-70C, the objective optical system includes, in orderfrom the object side, the first unit G1 with a negative refractingpower, the second unit G2 with a positive refracting power, the thirdunit G3 with a negative refracting power, and the fourth unit G4 with apositive refracting power, and has a positive refracting power as awhole.

The fourth unit G4 is constructed with the positive lens L1 and theprism P1. The eyepiece optical system is constructed with the positivelens E1 and the prism P and has a positive refracting power as a whole.

The image erecting means includes the prism P1 and the prism P. In thereal image mode finder optical system of the twenty-fourth embodiment,the intermediate image formed by the objective optical system isinterposed between the prism P1 and the positive lens E1, and the fieldframe, such as that shown in FIG. 4, is provided in the proximity of itsimaging position.

The magnification of the finder is changed in the range from thewide-angle position to the telephoto position by fixing the first unitG1 and the fourth unit G4 and by simply moving the second unit G2 towardthe object side and the third unit G3 toward the eyepiece side along theoptical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 isconstructed with a single lens. The entrance surface of the prism P1 hasa curvature. The entrance surface and the exit surface of the prism Palso have curvatures.

The prism P1 and the prism P are provided with reflecting surfaces alongthe optical path so that the optical axis is bent to obtain an erectimage. For example, the prism P1 is provided with three reflectingsurfaces for bending the optical axis once in the Y-Z plane and twice inthe X-Y plane in this order from the object side, and the prism P isprovided with one reflecting surface for bending the optical axis in theY-Z plane to erect the image. Also, the arrangement of the reflectingsurfaces is based on that of a Porro prism. Angles made with the opticalaxis bent by the reflecting surfaces are such that, for example, theangles of the optical axis bent by the reflecting surfaces of the prismP1 are smaller than 90 degrees. The three reflecting surfaces of theprism P1 are coated with metal films, such as silver and aluminum. Thereflecting surface of the prism P utilizes total reflection.

However, the ways of bending the optical axis through the prisms and theangles of the optical axis bent by the reflecting surfaces are notlimited to the above description. For example, the angle of the opticalaxis bent by the most field-frame-side reflecting surface of the prismP1 may be made smaller than 90 degrees so that this reflecting surfaceis coated with a metal film. Moreover, the angle of the optical axisbent by the second reflecting surface, from the field frame side, of theprism P1 may also be made larger than 90 degrees so that this reflectingsurface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can bemade in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the realimage mode finder optical system according to the twenty-fourthembodiment are shown below.

Numerical data 24 Wide-angle position Middle position Telephoto positionm  0.457  0.775  1.602 ω (°) 30.208 17.858  8.701 f (mm)  8.505 14.41229.797 Pupil dia. (mm)  4.000 r₁ = 75.2465 d₁ = 1.0000 n_(d1) = 1.58423ν_(d1) = 30.49 r₂ = 8.8816 (aspherical) d₂ = D2 (variable) r₃ = 10.2728(aspherical) d₃ = 4.1473 n_(d3) = 1.52542 ν_(d3) = 55.78 r₄ = −18.0037(aspherical) d₄ = D4 (variable) r₅ = −10.0864 (aspherical) d₅ = 1.0000n_(d5) = 1.58425 ν_(d5) = 30.35 r₆ = 10.3864 (aspherical) d₆ = D6(variable) r₇ = 19.6921 d₇ = 4.3014 n_(d7) = 1.52542 ν_(d7) = 55.78 r₈ =−13.1461 (aspherical) d₈ = 0.5000 r₉ = 21.4624 (aspherical) d₉ = 27.5577n_(d9) = 1.52542 ν_(d9) = 55.78 r₁₀ = ∞ d₁₀ = 2.1330 r₁₁ = ∞ (fieldframe) d₁₁ = 8.3794 r₁₂ = 18.8914 (aspherical) d₁₂ = 3.1249 n_(d12) =1.52542 ν_(d12) = 55.78 r₁₃ = −18.8429 d₁₃ = 2.5000 r₁₄ = −19.8984(aspherical) d₁₄ = 14.0000 n_(d14) = 1.52542 ν_(d14) = 55.78 r₁₅ =−12.6982 (aspherical) d₁₅ = 16.9541 r₁₆ = ∞ (eyepoint) Asphericalcoefficients Second surface K = −1.2958 A₄ = 3.44925 × 10⁻⁶ A₆ = 4.20426× 10⁻⁷ A₈ = −7.66223 × 10⁻⁹ Third surface K = −0.2616 A₄ = −2.70426 ×10⁻⁴ A₆ = 1.77644 × 10⁻⁶ A₈ = −2.00847 × 10⁻⁷ Fourth surface K = −0.0223A₄ = −7.38297 × 10⁻⁵ A₆ = 6.70806 × 10⁻⁷ A₈ = −1.54652 × 10⁻⁷ Fifthsurface K = 0.2135 A₄ = 3.49998 × 10⁻⁴ A₆ = −1.71207 × 10⁻⁵ A₈ = 3.68862× 10⁻⁷ Sixth surface K = −0.0430 A₄ = −1.78394 × 10⁻⁴ A₆ = −7.98576 ×10⁻⁶ A₈ = 1.76981 × 10⁻⁷ Eighth surface K = 0.1579 A₄ = 4.99038 × 10⁻⁶A₆ = 8.82927 × 10⁻⁷ A₈ = 1.18585 × 10⁻⁸ Ninth surface K = 0.0120 A₄ =−1.28730 × 10⁻⁴ A₆ = 5.21275 × 10⁻⁷ Twelfth surface K = 0.0000 A₄ =−2.49634 × 10⁻⁴ A₆ = 1.72455 × 10⁻⁷ A₈ = 2.31794 × 10⁻⁹ Fourteenthsurface K = 0.0000 A₄ = 8.06332 × 10⁻⁶ A₆ = 4.07603 × 10⁻⁷ A₈ = −1.41628× 10⁻⁸ Fifteenth surface K = 0.0000 A₄ = 3.96776 × 10⁻⁵ A₆ = 5.11111 ×10⁻⁸ A₈ = −1.38979 × 10⁻¹⁰ Wide-angle Middle Telephoto position positionposition Zoom data D2  11.4348  8.0329  4.3575 D4  1.2500  6.8862 14.8224 D6  8.1779  5.9436  1.6828 mh = 9.391 mm f123 −10.255 −17.402−36.720 m23  0.592  1.000  2.070 m2  −1.000 m3  −1.000 Condition (9)MG45 −0.831  −0.834  −0.837 Conditions (1), (7) mh/fe = 0.505 Conditions(2), (3) fe = 18.603 mm Condition (8) φ (mh/2) = −0.118345 (1/mm)Condition (10) β3 = −1.000 Condition (11) SF2 = −0.273 Condition (12)F2/f3 = −1.524 Condition (13) fw/fFw = −0.829 Condition (14) fT/fFT =−0.811 Condition (15) mT/mW = 3.503 Condition (16) fw/fW123 = −0.829Condition (17) fT/fT123 = −0.811

The real image mode finder optical system according to the presentinvention constructed as mentoned above can be used in any of variousphotographing apparatuses, such as compact cameras, for example, 35 mmfilm cameras and APS film cameras; digital cameras using electronicimage sensors, for example, CCDs and CMOS sensors; and video movies. Aspecific application example of this finder optical system will bedescribed below.

FIGS. 71-73 show an example of an electronic camera incorporating thereal image mode finder optical system of the present invention.

As shown in FIGS. 71-73, an electronic camera 200 includes aphotographing optical system 202 having a photpgraphing optical path201, a finder optical system 204 of the present invention having afinder optical path 203, a release button 205, a stroboscopic lamp 206,and a liquid crystal display monitor 207. When the release button 205provided on the upper surface of the electronic camera 200 is pushd,photographing is performed through the photographing optical system 202in association with the release button 205. An object image formed bythe photographing optical system 202 falls on an image senser chip 209,such as a CCD, through various filters 208, such as an IR (infrared)cutoff filter and a low-pass filter.

The object image received by the image sensor chip 209 is displayed, asan electronic image, on the liquid crystal display monitor 207 providedon the back surface of the electronic camera 200 through a processingmeans 211 electrically connected with terminals 210. The processingmeans 211 controls a recording means 212 for recording the object imagereceived by the image sensor chip 209 as electronic information. Therecording means 212 is electrocally connected with the processing means211. Also, the recording means 212 may be replaced with a device forwriting the record in a recording medium, such as a floppy disk, a smartmedium, or memory card.

Where the photographing optical system 202 is constructed as a zoomlens, the finder optical system 204 having the finder optical path 203may use the real image mode finder optical system of any of the aboveembodiments. Where the photographing optical system 202 is a singlefocus optical system, the objective optical system in the finder opticalsystem 204 may be replaced with a single focus objective optical systemin which a photographing area can be observed.

For the image erecting means, any means which is capable of erecting animage, not to speak of the Porro prism, is satisfactory. For example,when a roof reflecting surface is used as the image erecting means sothat the objective optical system includes the roof reflecting surfaceand one planar reflecting surface and the eyepiece optical systemincludes one planar reflecting surface, compactness of the entire cameracan be achieved. The reflecting surfaces are not limited to planarsurfaces and may be configured as curved surfaces.

Even when a photographing film is used instead of the image sensor chip209, a compact film camera with an excellent view can be obtained.

FIGS. 74A-74C show a specific example of a photographing zoom lens usedin a compact camera for a 35 mm film (the maximum image height of 21.6mm).

The photographing zoom lens includes, in order from the object side, thefirst unit G1 with a positive refracting power; the second unit G2 witha negative refracting power, having an aperture stop S which is variablein aperture diameter, at the most object-side position; and the thirdunit G3 with a negative refracting power. When the magnification of thefinder is changed in the range from the wide-angle position to thetelephoto position, a space between the first unit and the second unitis continuously widened, and a space between the second unit and thethird unit is contunuously narrowed, so that the first unit and thethird unit are integrally constructed and the first unit, the secondunit, and the third unit are continuously moved toward the object side,thereby forming the object image on a film surface.

Subsequently, numerical data of optical members constituting thephotographing zoom lens are shown below. In the numerical data, frepresents the focal length of the photographing zoom lens, ω representsa half angle of view, Fno represents an F-number, and bf represents aback focal distance. Other symbols are the same as those used in thenumerical data of the embodiments.

Numerical data (photographing zoom lens) Wide-angle position Middleposition Telephoto position f (mm) 29.31 72.87 135.00 ω (°) 28.3 16.1 9.0 Fno  4.1  6.8  11.5 bf (mm)  9.47732 31.48343  71.3185 r₁ =−180.6198 d₁ = 1.2001 n_(d1) = 1.76182 ν_(d1) = 26.52 r₂ = 180.6198 d₂ =0.2286 r₃ = 21.6168 d₃ = 3.1212 n_(d3) = 1.49700 ν_(d3) = 81.54 r₄ =−380.8986 d₄ = D4 (variable) r₅ = ∞ (stop) d₅ = 1.0000 r₆ = −16.3795 d₆= 1.0004 n_(d6) = 1.77250 ν_(d6) = 49.60 r₇ = 12.8963 d₇ = 3.1001 n_(d7)= 1.72825 ν_(d7) = 28.46 r₈ = −134.5936 d₈ = 0.4702 r₉ = 31.9527 d₉ =3.3010 n_(d9) = 1.56016 ν_(d9) = 60.30 r₁₀ = −24.8940 (aspherical) d₁₀ =0.7899 r₁₁ = −80.7304 d₁₁ = 1.0020 n_(d11) = 1.80518 ν_(d11) = 25.43 r₁₂= 21.6465 d₁₂ = 4.0740 n_(d12) = 1.69680 ν_(d12) = 55.53 r₁₃ = −17.2293d₁₃ = D13 (variable) r₁₄ = −48.1099 (aspherical) d₁₄ = 0.2501 n_(d14) =1.52288 ν_(d14) = 52.50 r₁₅ = −65.5251 d₁₅ = 1.3535 n_(d15) = 1.80610ν_(d15) = 40.95 r₁₆ = 47.5056 d₁₆ = 0.2911 r₁₇ = 41.0817 d₁₇ = 3.5899n_(d17) = 1.80518 ν_(d17) = 25.43 r₁₈ = −76.4471 d₁₈ = 3.8912 r₁₉ =−14.7089 d₁₉ = 1.6801 n_(d19) = 1.69680 ν_(d19) = 55.53 r₂₀ = −488.7372d₂₀ = D20 (variable) r₂₁ = ∞ (film surface) Aspherical coefficientsTenth surface K = 1.5373 A₄ = 8.3473 × 10⁻⁵ A₆ = 5.1702 × 10⁻⁷ A₈ =−1.3021 × 10⁻⁸ A₁₀ = 1.5962 × 10⁻¹⁰ Fourteenth surface K = −18.4065 A₄ =2.4223 × 10⁻⁵ A₆ = 1.3956 × 10⁻⁷ A₈ = −1.8237 × 10⁻¹⁰ A₁₀ = 3.9911 ×10⁻¹² Zoom data Wide-angle position Middle position Telephoto positionWhen an infinite object point is focused: D4  3.6815 10.0332 14.0700 D1311.5705  5.2188  1.1820 D20  9.4773 31.4834 71.3185 When the objectpoint distance is 0.6 m: D4  2.3504  8.3489 11.9918 D13 12.9016  6.9031 3.2602 D20  9.4773 31.4834 71.3185

1. A real image mode finder optical system comprising, in order from anobject side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said objective optical system hasimage erecting means including four reflecting surfaces, and wherein afocal length of said objective optical system is variable, and when amagnification of said finder optical system is changed, at least twolens units are moved along different paths and a focal length of saidobjective optical system at a wide-angle position thereof is shorterthan a focal length of said eyepiece optical system, said real imagemode finder optical system satisfying the following condition:0.52>mh/fe>1  where mh is a maximum width of said field frame and fe isa focal length of said eyepiece optical system.
 2. A real image modefinder optical system comprising, in order from an object side: anobjective optical system with a positive refracting power; a field framelocated in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said objective optical system has an imageerecting device including four reflecting surfaces, and wherein a focallength of said objective optical system is variable, and when amagnification of said finder optical system is changed, at least twolens units are moved along different paths and a focal length of saidobjective optical system at a wide-angle position thereof is shorterthan a focal length of said eyepiece optical system.
 3. A real imagemode finder optical system according to claim 1, wherein said objectiveoptical system includes, in order from said object side, a first unitwith a negative power, moved when said magnification is changed; asecond unit with a positive power, moved when said magnification ischanged; a third unit with a negative power, moved when saidmagnification is changed; and a fourth unit with a positive power, fixedwhen said magnification is change and including three reflectingsurfaces.
 4. A real image mode finder optical system according to claim3, wherein said fourth unit includes two prisms so that each of saidprisms has at least one reflecting surface and one of an entrancesurface and an exit surface of each prism is configured as a curvedsurface with finite curvature.
 5. A real image mode finder opticalsystem according to claim 4, wherein at least one of said two prisms hastotally reflecting surfaces.
 6. A real image mode finder optical systemaccording to claim 4, wherein each of said first unit, said second unit,and said third unit is constructed with a single lens.
 7. A real imagemode finder optical system constructed to be independent of aphotographing optical system, comprising, in order from an object side:an objective optical system with a positive refracting power; a fieldframe located in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes an image erecting device and wherein said objective opticalsystem is capable of having a focal length shorter than a focal lengthof said eyepiece optical system, and said eyepiece optical system has atleast one lens element so that a most observer's pupil-side lens elementsatisfies the following condition:ν>70  where ν is an Abbe's number of said most observer's pupil-sidelens element.
 8. A real image mode finder optical system constructed tobe independent of a photographing optical system, comprising, in orderfrom an object side: an objective optical system with a positiverefracting power; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system includes an image erecting device and wherein saidobjective optical system is capable of having a focal length shorterthan a focal length of said eyepiece optical system, and said eyepieceoptical system has at least one lens element to satisfy the followingconditions:0.52<mh/fe<1ν>70  where mh is a maximum width of said field frame, fe is a focallength of said eyepiece optical system, and ν is an Abbe's number of amost observer's pupil-side lens element.
 9. A photographing apparatusprovided with a real image mode finder optical system constructed to beindependent of a photographing optical system, comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes an image erecting device and wherein said objectiveoptical system is capable of having a focal length shorter than a focallength of said eyepiece optical system, and said eyepiece optical systemhas at least one lens element so that a most observer's pupil-side lenselement satisfies the following condition:ν>70  where ν is an Abbe's number of said most observer's pupil-sidelens element.
 10. A real image finder optical system constructed to beindependent of a photographing optical system, comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes an image erecting device, and wherein said eyepieceoptical system has at least one lens element so that a most observer'spupil-side lens element satisfies the following condition:υ>70  where υ is an Abbe's number of said most observer's pupil-sidelens element.
 11. A real image mode finder optical system constructed tobe independent of a photographing optical system, comprising, in orderfrom an object side: an objective optical system with a positiverefracting power; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system includes an image erecting device, and whereinsaid eyepiece optical system has at least one lens element to satisfythe following conditions:0.52<mh/fe<1υ>70  where mh is a maximum width of said field frame, fe is a focallength of said eyepiece optical system, and υ is an Abbe's number of amost observer's pupil-side lens element.
 12. A photographing apparatusprovided with a real image mode finder optical system constructed to beindependent of a photographing optical system, comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes an image erecting device, and wherein said eyepieceoptical system has at least one lens element so that a most observer'spupil-side lens element satisfies the following condition:υ>70  where υ is an Abbe's number of said most observer's pupil-sidelens element.
 13. A real image mode finder optical system constructed tobe independent of a photographing optical system, comprising, in orderfrom an object side: an objective optical system with a positiverefracting power; a field frame located in the proximity of an imagingposition of said objective optical system; and an eyepiece opticalsystem with a positive refracting power, wherein said real image modefinder optical system includes an image erecting device, and whereinsaid objective optical system is capable of having a focal lengthshorter than a focal length of said eyepiece optical system, and saideyepiece optical system has at least one lens element that satisfies thefollowing condition:υ>70  where υ is an Abbe's number of said at least one lens element. 14.A real image finder optical system constructed to be independent of aphotographing optical system, comprising, in order from an object side:an objective optical system with a positive refracting power; a fieldframe located in the proximity of an imaging position of said objectiveoptical system; and an eyepiece optical system with a positiverefracting power, wherein said real image mode finder optical systemincludes an image erecting device, and wherein said objective opticalsystem is capable of having a focal length shorter than a focal lengthof said eyepiece optical system, and said eyepiece optical system has atleast one lens element that satisfies the following conditions:0.52<mh/fe<1υ>70  where mh is a maximum width of said field frame, fe is a focallength of said eyepiece optical system, and υ is an Abbe's number of asaid at least one lens element.
 15. A photographing apparatus providedwith a real image mode finder optical system constructed to beindependent of a photographing optical system, comprising, in order froman object side: an objective optical system with a positive refractingpower; a field frame located in the proximity of an imaging position ofsaid objective optical system; and an eyepiece optical system with apositive refracting power, wherein said real image mode finder opticalsystem includes an image erecting device, and wherein said objectiveoptical system is capable of having a focal length shorter than a focallength of said eyepiece optical system, and said eyepiece optical systemhas at least one lens element that satisfies the following condition:υ>70  where υ is an Abbe's number of said at least one lens element.